This is a catch-all PR that modernizes and updates our Stylelint config, and resolves all open issues. This is a pretty big change - so I want to update all of our related dependencies in lockstep.

In particular, this PR

- [x] updates stylelint to `v14`
- [x] adds in the standard stylelint config for SCSS (`stylelint-config-standard-scss`)
- [x] swaps out `stylelint-config-prettier` for `stylelint-config-prettier-scss`
- [x] ~~properly update `@primer`-related plugins:~~ completely remove `primer` from our configuration
- [x] autofix, manually resolve, or disable all newly-introduced lint errors; **I've avoided manually resolving errors that would be a behavioural change**
- [x] re-runs `npm run format`

See the "next steps" section on some extra thoughts on disabling errors.

(implicitly, I'm also using node 16/the new package-lock format).

### disabling rules and next steps

I've introduced several new disabled rules. Let me quickly explain what's going on; there are two categories of rules I've disabled:

1. rules that were temporary disables; they were frequent enough that I couldn't manually resolve them, but should be simple. **I plan on opening issues to re-enable each of these rules**, just after this PR
    - `declaration-block-no-redundant-longhand-properties`: this is just tedious and error-prone
    - `no-descending-specificity`: this one is tricky since it could have impacts on the cascade (though that seems unlikely)
    - `scss/no-global-function-names`: I think we need to [import map and then use `map.get`](https://stackoverflow.com/questions/64210390/sass-map-get-doesnt-work-map-get-does-what-gives), but I'll leave this as out of scope for now
2. rules that are long-term disables; due to the SASS-based nature of our theme, I think we'll keep these in limbo
    - `alpha-value-notation` causes problems with SASS using the `modern` syntax - literals like `50%` are not properly interpolated, and they cause formatting issues on the site
    - `color-function-notation` also causes problems with SASS, but in this case the `modern` syntax breaks SASS compilation; we're not alone (see this [SO post](https://stackoverflow.com/questions/71805735/error-function-rgb-is-missing-argument-green-in-sass)). 

In addition, we have many inline `stylelint-disable` comments. I'd open a separate issue to audit them, especially since I think some disables are unnecessary.

### on Primer 

**note: there hasn't been much other discussion, so I'm going to remove primer's stylelint config.**

If I do add `@primer/stylelint-config`, I get *a ton* of errors about now using `@primer`'s in-built SCSS variables. I imagine that we probably won't want to use these presets (though I could be wrong). In that case, I think we could either:

1. disable all of those rules
4. not use `@primer/stylelint-config`, since we're not actually using primer, and shift back to the standard SCSS config provided by Stylelint

~~Any thoughts here? I also don't have the original context as to why we do use the primer rules, perhaps @pmarsceill can chime in?~~

- add an extra filter to children-list to fix #854
- strengthen condition for assignment to first_level_url

Tested with Jekyll 3.9.2 and 4.2.2

Note: Jekyll 3.9.2 doesn't support `| where: "grand_parent:  nil"`

This is a PR with three key changes:

1. Consolidate two identical CI files, `ci.yml` and `ci-master.yml` into one file
2. Consolidate two almost-identical jobs (`jekyll-build-*`) into one job with a strategy matrix
3. Update various dependencies/platforms
    * Node: `12.x` -> `16.x` (only in CI); `12.x` has been EOL for a while
    * Ruby: `2.6` -> `2.7`; `2.6` just reached EOL
    * `actions/checkout` -> `v2` -> `v3`
    * switches `jekyll/builder` to `jekyll/jekyll`, since we don't actually use any of the features in `jekyll/builder`

## on our CI philosophy

In working on this, I have a couple of questions:

1. We don't actually use our `Dockerfile` that we provide. Does this make sense? Should we be running CI with this instead?
2. Is there a specific reason that we're using `jekyll/jekyll`? Notably, this isn't an official package, but a community-driven one. Does it match what's used by GitHub Pages?
3. Do we have to use any docker image at all? For example, what if we just rely on the `setup-ruby` action?
    * one advantage of this is that it's much easier for us to test across multiple OS versions; we just need to have a strategy matrix for OS and do windows, macos, ubuntu, etc.
    * another advantage is that we can easily test different ruby versions in conjunction with different jekyll versions

Eventually, I would like to see us test across:

* different Jekyll versions
* different OSes
* different Ruby versions

but perhaps that might be too aggressive. Happy for any feedback on this PR or those questions!

without overflow-x: auto; a very long line of code will overflow the box and look awkward


Co-authored-by: Matt Wang <matt@matthewwang.me>

partially a commit to start generating Netlify previews on arbitrary branches!

Based on #238, resolves #66.

Closes #825


Co-authored-by: Matt Wang <matt@matthewwang.me>

I have a site whose content is written in AsciiDoc, using the [jekyll-asciidoc][] plugin.

Just the Docs works great, but there are just two minor styling glitches I've noticed:

The first is that Just the Docs' CSS doesn't understand the code block markup jekyll-asciidoc produces.  It's not too different though, so it's very easily fixed.

The second is that jekyll-asciidoc generates `div.sect(𝑛 − 1)` elements around headings of type `h𝑛`, that enclose all the heading and all the content after it until the next heading of greater or equal rank.

This means that headings are _always_ first children in AsciiDoc output, which meant the wrong margins were applied to most headings. To fix this, we need to only reduce the margin of first-child headings nested directly below the .main-content element, and headings nested directly below AsciiDoc `.sect𝑛` elements that are themselves first children.

With these two small changes, my site looks perfect, and the styles look exactly the same as on Just the Docs' own documentation.

[jekyll-asciidoc]: https://github.com/asciidoctor/jekyll-asciidoc

Co-authored-by: Matt Wang <matt@matthewwang.me>

The anchor heading item is keyboard focusable, but when focused and not hovered, it is not visible. This PR fixes that. Also, great project!

**Rationale**
I would like to customize the site footer content without needing to override the entire default layout. Ideally, I'd like to shorten the attribution to something like "Built with Just the Docs"

**Implementation**
Create a new `site_footer.html` include that users can override.

**Possible changes**
I debated whether or not the `<footer class="site-footer">` should be in/out of the include. I opted for placing it inside the include so I have the option of disabling the footer entirely by creating an empty site_footer file in my site.

Co-authored-by: Matt Wang <matt@matthewwang.me>
Co-authored-by: Patrick Marsceill <pmarsceill@users.noreply.github.com>

Fixes #488.
- Replace `''` by `""` in rake script and resulting search data file.
Tested on macOS Catalina.

Set `child_nav_order` to `desc` to reverse the sort order for a child section.

Co-authored-by: Matt Wang <matt@matthewwang.me>

Looking at how the variables are defined in _variables.scss, with various dependencies between them aimed at ensuring a consistent color scheme, one might expect that redefining a given variable would affect the remaining styles that depend on it.

This is not the case, however, due to the order in which the files are processed. This PR edits the documentation to mention the non-propagating behavior of redefined variables, to better guide users that wish to customize the site using custom themes, and call their attention to the need to redefine the dependency relations as well.

Co-authored-by: Matt Wang <matt@matthewwang.me>
Co-authored-by: Patrick Marsceill <pmarsceill@users.noreply.github.com>

* implements search placeholder configuration

* changes implementation approach to use search_placeholder_custom

Thanks to @pdmosses for the suggestion!

* strips whitespace and HTML for both placeholder and aria-label

Fix #685
- Wrap scss file in comments with `{% raw %}` and `{% endraw %}` tags

Co-authored-by: Matt Wang <matt@matthewwang.me>

Fix #517

Users expect nested task lists to have the same indentation as other lists.
Fix the styling in `_sass/content.scss` to do that.
Add examples in `docs/index-test.md` to test.

As is, this is invalid and will not cause the TOC to be rendered. The collapsing example is fine.

Co-authored-by: Matt Wang <matt@matthewwang.me>
Co-authored-by: Peter Mosses <18308236+pdmosses@users.noreply.github.com>

These docs outline some of the custom includes that are provided by the theme and can be modified by the user.

Co-authored-by: Matt Wang <matt@matthewwang.me>
Co-authored-by: Patrick Marsceill <pmarsceill@users.noreply.github.com>

* Show how to break an ol

Close #750

The theme uses CSS counters for ordered lists.
So to continue the numbering of an ordered list after a break,
use `style="counter-reset:none"` instead of `start="42"`.
Add the example from #750 to `docs/index-test.md` to test.

* Show how to start from 42

Close #750

The theme uses CSS counters for ordered lists.
To start the numbering of an ordered list with 42,
use `{:style="counter-reset:step-counter 41"}` instead of `start="42"`.

Add the example from #750 to `docs/index-test.md` to test.

This PR combines (and resolves conflicts between) #448, #463, #466, #494, #495, #496, #498, and #572. 

The main aim is to facilitate use of several of the implemented features _together_, when using the fork as a remote theme. It should also simplify merging the included PRs into a future release.

The branch [combination-rec-nav](https://github.com/pdmosses/just-the-docs/tree/combination-rec-nav) adds [multi-level navigation](https://github.com/pmarsceill/just-the-docs/pull/462) and (NEW:) [sibling links](https://github.com/pmarsceill/just-the-docs/pull/394) to the branch used for this PR. It includes updated [documentation for the navigation structure](https://pdmosses.github.io/just-the-docs/docs/navigation-structure/), and reorganised and extended [navigation tests](https://pdmosses.github.io/just-the-docs/tests/navigation/). The documentation and the tests can be browsed at the (temporary) [website published from the combination-rec-nav branch](https://pdmosses.github.io/just-the-docs/

).

_Caveat:_ The changes to v0.3.3 in this PR and #462 have not yet been reviewed or approved, and may need updating before merging into a release of the theme. If you use a branch from a PR as a remote theme, there is a risk of such updates affecting your website. Moreover, these branches are likely to be deleted after they have been merged. To avoid  such problems, you could copy the branch that you want to use to your own fork of the theme.

Co-authored-by: Matt Wang <matt@matthewwang.me>

Bumps [prettier](https://github.com/prettier/prettier) from 2.6.2 to 2.7.1.
- [Release notes](https://github.com/prettier/prettier/releases)
- [Changelog](https://github.com/prettier/prettier/blob/main/CHANGELOG.md)
- [Commits](https://github.com/prettier/prettier/compare/2.6.2...2.7.1

)

---
updated-dependencies:
- dependency-name: prettier
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

This PR adds a small link back to Netlify in the footer (specifically, in the user-editable config); this is a necessary prerequisite for the [Netlify OSS Plan](https://www.netlify.com/legal/open-source-policy). 

See: https://github.com/orgs/just-the-docs/teams/maintainers/discussions/1/comments/18.

Bumps [prettier](https://github.com/prettier/prettier) from 2.5.1 to 2.6.2.
- [Release notes](https://github.com/prettier/prettier/releases)
- [Changelog](https://github.com/prettier/prettier/blob/main/CHANGELOG.md)
- [Commits](https://github.com/prettier/prettier/compare/2.5.1...2.6.2

)

---
updated-dependencies:
- dependency-name: prettier
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

This is one solution for #798, namely that `webrick` is needed as an explicit dependency for Ruby 3+.

Closes #798.

updates Code of Conduct to Contributor Covenant v2.1

See - https://www.contributor-covenant.org/version/2/1/code_of_conduct/

* Set color for search input

Fix #497
- Insert `color: $body-text-color;` in styling for `search-input`.

* Update search.scss

Prettier

Co-authored-by: Matt Wang <matt@matthewwang.me>

Co-authored-by: Matt Wang <matt@matthewwang.me>

Co-authored-by: Matt Wang <matt@matthewwang.me>

Co-authored-by: Matt Wang <matt@matthewwang.me>

Bumps [prettier](https://github.com/prettier/prettier) from 2.1.2 to 2.5.1.
- [Release notes](https://github.com/prettier/prettier/releases)
- [Changelog](https://github.com/prettier/prettier/blob/main/CHANGELOG.md)
- [Commits](https://github.com/prettier/prettier/compare/2.1.2...2.5.1

)

---
updated-dependencies:
- dependency-name: prettier
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>