Docs: Fix categories to sort by title instead of filename

The default seems to be sorted by filename, which would be good
enough if it weren't for the fact that it includes the `.md` file
extension, and thus, after we introduced `test.each.md`, the sorting
was:

* test.each
* test
* test.only
* test.skip
* test.todo

because `each` < `md`:

* test.each.md
* test.md
* test.only.md
* test.skip.md
* test.todo.md

Fix by adding an explicit sort for the `title` key.

Ref #1569.

docs/_layouts/category.html

@@ -8,7 +8,7 @@
     <h2>{{ page.title }}</h2>
 
     <ul class="page-list">
-    {% assign pages = site.pages | where:'categories', page.category %}
+    {% assign pages = site.pages | where: 'categories', page.category | sort_natural: 'title' %}
     {% for page in pages %}
     <li class="page-item">
         <h3><a href="{{ page.url }}">{{page.title}}</a></h3>

docs/_layouts/default.html

@@ -5,7 +5,7 @@
 <section class="sidebar">
     <h4>Main methods</h4>
     <ul class="sidebar-list">
-    {% assign methods = site.pages | where:'categories', 'main' %}
+    {% assign methods = site.pages | where: 'categories', 'main' | sort_natural: 'title' %}
     {% for entry in methods %}
     <li class="sidebar-item{% if entry.url == page.url %} sidebar-item-active{% endif %}">
         <a href="{{ entry.url }}">{{entry.title}}</a>
@@ -15,7 +15,7 @@ <h4>Main methods</h4>
 
     <h4>Assertions</h4>
     <ul class="sidebar-list">
-    {% assign assertions = site.pages | where:'categories', 'assert' %}
+    {% assign assertions = site.pages | where: 'categories', 'assert' | sort_natural: 'title' %}
     {% for entry in assertions %}
     <li class="sidebar-item{% if entry.url == page.url %} sidebar-item-active{% endif %}">
         <a href="{{ entry.url }}">{{entry.title}}</a>
@@ -26,7 +26,7 @@ <h4>Assertions</h4>
     <h4>Configuration tools</h4>
 
     <ul class="sidebar-list">
-    {% assign config = site.pages | where:'categories', 'config' %}
+    {% assign config = site.pages | where: 'categories', 'config' | sort_natural: 'title' %}
     {% for entry in config %}
     <li class="sidebar-item{% if entry.url == page.url %} sidebar-item-active{% endif %}">
         <a href="{{ entry.url }}">{{entry.title}}</a>
@@ -37,7 +37,7 @@ <h4>Configuration tools</h4>
     <h4>Callback events</h4>
 
     <ul class="sidebar-list">
-    {% assign callbacks = site.pages | where:'categories', 'callbacks' %}
+    {% assign callbacks = site.pages | where: 'categories', 'callbacks' | sort_natural: 'title' %}
     {% for entry in callbacks %}
     <li class="sidebar-item{% if entry.url == page.url %} sidebar-item-active{% endif %}">
         <a href="{{ entry.url }}">{{entry.title}}</a>
@@ -48,7 +48,7 @@ <h4>Callback events</h4>
     <h4>Async control</h4>
 
     <ul class="sidebar-list">
-    {% assign async = site.pages | where:'categories', 'async' %}
+    {% assign async = site.pages | where: 'categories', 'async' | sort_natural: 'title' %}
     {% for entry in async %}
     <li class="sidebar-item{% if entry.url == page.url %} sidebar-item-active{% endif %}">
         <a href="{{ entry.url }}">{{entry.title}}</a>