Implement MathJax

If a post needs to render math equations, it only has
to include the mathjax.json params.

layout/item.html

@@ -1,11 +1,13 @@
-<div class="post-list-item">
-<h3><a class="post-title" href="/{{ slug }}.html">{{ title }}</a></h3>
+<div class="horizontal-center">
+    <div class="post-list-item">
+        <h2><a class="post-title" href="/{{ slug }}.html">{{ title }}</a></h2>
 
-<p><b>&gt; {{ date }}</b></p>
+        <p><b>&gt; {{ date }}</b></p>
 
-<p class="post-summary">
-    <div class="quote">
-        {{ summary }}...
+        <p class="post-summary">
+            <div class="quote text">
+                {{ summary }}...
+            </div>
+        </p>
     </div>
-</p>
 </div>