vendor: update `jekyll-anchor-headings`, `lunr.js` (#1071)

Closes #1070.

This PR:

- updates `jekyll-anchor-headings` to `1.0.12`; this was a simple copy-paste
- updates `lunr.js` to `2.3.9`; this was a bit more involved:
    - I didn't see a minified build in the repo, so I ran it through [DigitalOcean's minifier](https://www.digitalocean.com/community/tools/minify)
    - copyright notices weren't properly included in the previous minified build, so I:
        - include an actual copy of the original MIT License for `lunr.js`
        - includes proper attribution for other functions, which include derivative works

There's a tiny bundle size increase in `lunr.js` due to the comments, but I think that's reasonable given that it's related to licensing; still trivial in the grand scheme of things.

As an aside: it would be neat if we could include minification as part of the build pipeline instead!  

_includes/vendor/anchor_headings.html

@@ -24,7 +24,7 @@
     OTHER DEALINGS IN THE SOFTWARE.
   {% endcomment %}
   {% comment %}
-    Version 1.0.7
+    Version 1.0.12
       https://github.com/allejo/jekyll-anchor-headings
 
     "Be the pull request you wish to see in the world." ~Ben Balter
@@ -37,6 +37,8 @@
 
     Optional Parameters:
       * beforeHeading (bool)   : false  - Set to true if the anchor should be placed _before_ the heading's content
+      * headerAttrs   (string) :  ''    - Any custom HTML attributes that will be added to the heading tag; you may NOT use `id`;
+                                          the `%heading%` and `%html_id%` placeholders are available
       * anchorAttrs   (string) :  ''    - Any custom HTML attributes that will be added to the `<a>` tag; you may NOT use `href`, `class` or `title`;
                                           the `%heading%` and `%html_id%` placeholders are available
       * anchorBody    (string) :  ''    - The content that will be placed inside the anchor; the `%heading%` placeholder is available
@@ -46,6 +48,7 @@
       * h_max         (int)    :  6     - The maximum header level to build an anchor for; any header greater than this value will be ignored
       * bodyPrefix    (string) :  ''    - Anything that should be inserted inside of the heading tag _before_ its anchor and content
       * bodySuffix    (string) :  ''    - Anything that should be inserted inside of the heading tag _after_ its anchor and content
+      * generateId    (true)   :  false - Set to true if a header without id should generate an id to use.
 
     Output:
       The original HTML with the addition of anchors inside of all of the h1-h6 headings.
@@ -54,6 +57,7 @@
   {% assign minHeader = include.h_min | default: 1 %}
   {% assign maxHeader = include.h_max | default: 6 %}
   {% assign beforeHeading = include.beforeHeading %}
+  {% assign headerAttrs = include.headerAttrs %}
   {% assign nodes = include.html | split: '<h' %}
 
   {% capture edited_headings %}{% endcapture %}
@@ -84,17 +88,41 @@
 
     {% capture _closingTag %}</h{{ headerLevel }}>{% endcapture %}
     {% assign _workspace = node | split: _closingTag %}
-    {% assign _idWorkspace = _workspace[0] | split: 'id="' %}
-    {% assign _idWorkspace = _idWorkspace[1] | split: '"' %}
-    {% assign html_id = _idWorkspace[0] %}
-
     {% capture _hAttrToStrip %}{{ _workspace[0] | split: '>' | first }}>{% endcapture %}
     {% assign header = _workspace[0] | replace: _hAttrToStrip, '' %}
+    {% assign escaped_header = header | strip_html | strip %}
+
+    {% assign _classWorkspace = _workspace[0] | split: 'class="' %}
+    {% assign _classWorkspace = _classWorkspace[1] | split: '"' %}
+    {% assign _html_class = _classWorkspace[0] %}
+
+    {% if _html_class contains "no_anchor" %}
+      {% assign skip_anchor = true %}
+    {% else %}
+      {% assign skip_anchor = false %}
+    {% endif %}
+
+    {% assign _idWorkspace = _workspace[0] | split: 'id="' %}
+    {% if _idWorkspace[1] %}
+      {% assign _idWorkspace = _idWorkspace[1] | split: '"' %}
+      {% assign html_id = _idWorkspace[0] %}
+    {% elsif include.generateId %}
+      <!-- If the header did not have an id we create one. -->
+      {% assign html_id = escaped_header | slugify %}
+      {% if html_id == "" %}
+        {% assign html_id = false %}
+      {% endif %}
+      {% capture headerAttrs %}{{ headerAttrs }} id="%html_id%"{% endcapture %}
+    {% endif %}
 
     <!-- Build the anchor to inject for our heading -->
     {% capture anchor %}{% endcapture %}
 
-    {% if html_id and headerLevel >= minHeader and headerLevel <= maxHeader %}
+    {% if skip_anchor == false and html_id and headerLevel >= minHeader and headerLevel <= maxHeader %}
+      {% if headerAttrs %}
+        {% capture _hAttrToStrip %}{{ _hAttrToStrip | split: '>' | first }} {{ headerAttrs | replace: '%heading%', escaped_header | replace: '%html_id%', html_id }}>{% endcapture %}
+      {% endif %}
+
       {% capture anchor %}href="#{{ html_id }}"{% endcapture %}
 
       {% if include.anchorClass %}
@@ -102,14 +130,14 @@
       {% endif %}
 
       {% if include.anchorTitle %}
-        {% capture anchor %}{{ anchor }} title="{{ include.anchorTitle | replace: '%heading%', header }}"{% endcapture %}
+        {% capture anchor %}{{ anchor }} title="{{ include.anchorTitle | replace: '%heading%', escaped_header }}"{% endcapture %}
       {% endif %}
 
       {% if include.anchorAttrs %}
-        {% capture anchor %}{{ anchor }} {{ include.anchorAttrs | replace: '%heading%', header | replace: '%html_id%', html_id }}{% endcapture %}
+        {% capture anchor %}{{ anchor }} {{ include.anchorAttrs | replace: '%heading%', escaped_header | replace: '%html_id%', html_id }}{% endcapture %}
       {% endif %}
 
-      {% capture anchor %}<a {{ anchor }}>{{ include.anchorBody | replace: '%heading%', header | default: '' }}</a>{% endcapture %}
+      {% capture anchor %}<a {{ anchor }}>{{ include.anchorBody | replace: '%heading%', escaped_header | default: '' }}</a>{% endcapture %}
 
       <!-- In order to prevent adding extra space after a heading, we'll let the 'anchor' value contain it -->
       {% if beforeHeading %}
@@ -120,15 +148,15 @@
     {% endif %}
 
     {% capture new_heading %}
-      <h{{ _hAttrToStrip }}
-        {{ include.bodyPrefix }}
-        {% if beforeHeading %}
-          {{ anchor }}{{ header }}
-        {% else %}
-          {{ header }}{{ anchor }}
-        {% endif %}
-        {{ include.bodySuffix }}
-      </h{{ headerLevel }}>
+<h{{ _hAttrToStrip }}
+  {{ include.bodyPrefix }}
+  {% if beforeHeading %}
+    {{ anchor }}{{ header }}
+  {% else %}
+    {{ header }}{{ anchor }}
+  {% endif %}
+  {{ include.bodySuffix }}
+</h{{ headerLevel }}>
     {% endcapture %}
 
     <!--