Refactor post template

- add article tags around post content
- creates post header
- add conditionals for extra options in meta

lib/site_template/_layouts/post.html

@@ -1,9 +1,15 @@
 ---
 layout: default
 ---
-<h2>{{ page.title }}</h2>
-<p class="meta">{{ page.date | date_to_string }}</p>
-
 <div class="post">
-{{ content }}
+
+  <header class="post-header">
+    <h1>{{ page.title }}</h1>
+    <p class="meta">{{ page.date | date: "%b %-d, %Y" }}{% if page.author %} • {{ page.author }}{% endif %}{% if page.meta %} • {{ page.meta }}{% endif %}</p>
+  </header>
+
+  <article class="post-content">
+  {{ content }}
+  </article>
+
 </div>