docs; formatting and tidying

- quick clean up pass on layout and colors for clarity/legibility
- added logo to the sidebar
- fix various css things like a full height page when content is shorter, so the footer doesn't creep away from the bottom
- start using em instead of px for consistency across devices

doc/site/modules/core/template.html

@@ -20,6 +20,7 @@
 </header>
 <div class="page">
   <nav class="big">
+    <a href="./"><img src="../../wren.svg" class="logo"></a>
     <ul>
       <li><a href="../">Modules</a></li>
       <li><a href="./">core</a></li>