Update anchor_headings.html

Fixes a bug where content after headings in header elements disappeared.
Header elements are not currently used in JtD, but could make the HTML more semantic.

_includes/vendor/anchor_headings.html

 {% capture headingsWorkspace %}
   {% comment %}
-    Version 1.0.3
+    Copyright (c) 2018 Vladimir "allejo" Jimenez
+
+    Permission is hereby granted, free of charge, to any person
+    obtaining a copy of this software and associated documentation
+    files (the "Software"), to deal in the Software without
+    restriction, including without limitation the rights to use,
+    copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following
+    conditions:
+
+    The above copyright notice and this permission notice shall be
+    included in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+    OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+    HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+    WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+    OTHER DEALINGS IN THE SOFTWARE.
+  {% endcomment %}
+  {% comment %}
+    Version 1.0.7
       https://github.com/allejo/jekyll-anchor-headings
 
     "Be the pull request you wish to see in the world." ~Ben Balter
 
     Usage:
-      {% include anchor_headings.html html=content %}
+      {% include anchor_headings.html html=content anchorBody="#" %}
 
     Parameters:
       * html          (string) - the HTML of compiled markdown generated by kramdown in Jekyll
 
     Optional Parameters:
       * beforeHeading (bool)   : false  - Set to true if the anchor should be placed _before_ the heading's content
+      * 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
       * anchorClass   (string) :  ''    - The class(es) that will be used for each anchor. Separate multiple classes with a space
       * anchorTitle   (string) :  ''    - The `title` attribute that will be used for anchors
@@ -42,17 +68,22 @@
     {% assign nextChar = node | replace: '"', '' | strip | slice: 0, 1 %}
     {% assign headerLevel = nextChar | times: 1 %}
 
-    <!-- If the level is cast to 0, it means it's not a h1-h6 tag, so let's try to fix it -->
+    <!-- If the level is cast to 0, it means it's not a h1-h6 tag, so let's see if we need to fix it -->
     {% if headerLevel == 0 %}
-      {% if nextChar != '<' and nextChar != '' %}
+      <!-- Split up the node based on closing angle brackets and get the first one. -->
+      {% assign firstChunk = node | split: '>' | first %}
+
+      <!-- If the first chunk does NOT contain a '<', that means we've broken another HTML tag that starts with 'h' -->
+      {% unless firstChunk contains '<' %}
         {% capture node %}<h{{ node }}{% endcapture %}
-      {% endif %}
+      {% endunless %}
 
       {% capture edited_headings %}{{ edited_headings }}{{ node }}{% endcapture %}
       {% continue %}
     {% endif %}
 
-    {% assign _workspace = node | split: '</h' %}
+    {% 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] %}
@@ -64,7 +95,7 @@
     {% capture anchor %}{% endcapture %}
 
     {% if html_id and headerLevel >= minHeader and headerLevel <= maxHeader %}
-      {% capture anchor %}href="#{{ html_id}}" aria-labelledby="{{ html_id}}"{% endcapture %}
+      {% capture anchor %}href="#{{ html_id }}"{% endcapture %}
 
       {% if include.anchorClass %}
         {% capture anchor %}{{ anchor }} class="{{ include.anchorClass }}"{% endcapture %}
@@ -74,6 +105,10 @@
         {% capture anchor %}{{ anchor }} title="{{ include.anchorTitle | replace: '%heading%', header }}"{% endcapture %}
       {% endif %}
 
+      {% if include.anchorAttrs %}
+        {% capture anchor %}{{ anchor }} {{ include.anchorAttrs | replace: '%heading%', header | replace: '%html_id%', html_id }}{% endcapture %}
+      {% endif %}
+
       {% capture anchor %}<a {{ anchor }}>{{ include.anchorBody | replace: '%heading%', header | default: '' }}</a>{% endcapture %}
 
       <!-- In order to prevent adding extra space after a heading, we'll let the 'anchor' value contain it -->
@@ -93,8 +128,17 @@
           {{ header }}{{ anchor }}
         {% endif %}
         {{ include.bodySuffix }}
-      </h{{ _workspace | last }}
+      </h{{ headerLevel }}>
     {% endcapture %}
+
+    <!--
+    If we have content after the `</hX>` tag, then we'll want to append that here so we don't lost any content.
+    -->
+    {% assign chunkCount = _workspace | size %}
+    {% if chunkCount > 1 %}
+      {% capture new_heading %}{{ new_heading }}{{ _workspace | last }}{% endcapture %}
+    {% endif %}
+
     {% capture edited_headings %}{{ edited_headings }}{{ new_heading }}{% endcapture %}
   {% endfor %}
 {% endcapture %}{% assign headingsWorkspace = '' %}{{ edited_headings | strip }}