Minor consistency fixups

- use a `{{#tag}}{{/tag}}` block for tag in tag.hbs
- use two braces consistently for `{{title}}`
- use double quotes consistently for attributes (quote switching is unnecessary)

post.hbs

@@ -21,7 +21,7 @@
         <header class="post-header">
             <h1 class="post-title">{{title}}</h1>
             <section class="post-meta">
-                <time class="post-date" datetime="{{date format='YYYY-MM-DD'}}">{{date format="DD MMMM YYYY"}}</time> {{tags prefix=" on "}}
+                <time class="post-date" datetime="{{date format="YYYY-MM-DD"}}">{{date format="DD MMMM YYYY"}}</time> {{tags prefix=" on "}}
             </section>
         </header>