Add some basic typography, tweak the Markdown

This commit adds some basic type sizes, weights and spacing for HTML
elements scoped inside a `.documentation` container.

It also tweaks some of the Markdown so that it renders the same as it
does on Github.

app/templates/views/documentation.html

@@ -7,8 +7,8 @@
 {% block maincolumn_content %}
 
 <div class="grid-row">
-  <div class="column-two-thirds">
-    {{ body }}
+  <div class="column-two-thirds documentation">
+	{{ body }}
   </div>
 </div>