Remove docs/search.md.
Remove JTD's code of conduct, as we have our own code of conduct.

Remove all the old just-the-docs components, and replace with a
dependency on the just-the-docs Ruby Gem (v0.10).
There is an outstanding issue with the flip cards on the home page, due
to modifications to JTD's scss which enabled this.

Use Ruby 3.3 as default, and remove csv and base64 from Gemfile, as
these should be dependencies of just-the-docs, rather than our site.
Build failure is fixed in main branch of JTD, as of a few hours ago.

Clean up old files from JTD fork.

Closes #66

See merge request !27

Remove configuration files for linters.

Remove VSCode-specific files left over from JTD development, including
.devcontainer and .vscode directories.

Remove docker-related files, which don't appear to be used in
our own CI workflows.

Remove old markdown files, left over from just-the-docs's documentation.

Add warning about MRI image redaction/confidentiality.

See merge request !26

This reverts commit fec50c11

Substitute relative paths with absolute links.

See merge request !24