feat(mustache): Added group_by filter to templates

defaults/layouts/section_index.html

@@ -3,17 +3,17 @@
 <main>
   <h1>{{page_title}}</h1>
   {{&body}}
-  {{#by_year}}
+  {{#posts | group_by year}}
   <section>
-    <h2>{{year}}</h2>
+    <h2>{{key}}</h2>
     <ul>
-      {{#posts}} <li><a href="{{permalink}}">{{&title}}</a><span>{{#date_iso}}<time
+      {{#items}} <li><a href="{{permalink}}">{{&title}}</a><span>{{#date_iso}}<time
             datetime="{{date_iso}}">{{date_display}}</time>{{/date_iso}}</span>
       </li>
-      {{/posts}}
+      {{/items}}
     </ul>
   </section>
-  {{/by_year}}
+  {{/posts}}
 </main>
 {{/content}}
 {{/base}}