Move macros

Each edition now has their own macros, so create a macros.html for the third edition too. Since the utterances theme differs between editions, we need to move it from snippets.html to the edition-specific macros.html too.

blog/templates/edition-3/extra.html

@@ -1,6 +1,6 @@
 {% extends "edition-3/base.html" %}
 
-{% import "macros.html" as macros %}
+{% import "snippets.html" as snippets %}
 
 {% block title %}{{ page.title }} | {{ config.title }}{% endblock title %}
 
@@ -17,6 +17,6 @@
     <hr>
     <section>
         <h2>Comments</h2>
-        {{ macros::utterances() }}
+        {{ snippets::utterances() }}
     </section>
 {% endblock after_main %}