Update templates

The following updates are made:
- index.html now lists the site description along with X articles
- _list_item.html universalizes code for iterating over the articles
- _site_social.html is merged into base.html
- _google_search.html is added for custom search support
- _gosquared.html, _google_analytics.html have minor formatting changes
- archives.html displays a one page list of all articles
- period_archives.html is removed as it is not planned for implementation atm
- tags.html general clean up and tweaks
- base.html now has
  - full rss/atom feed support
  - disqus comment count support on links (not used yet)
  - blog links in aside
  - search in aside

templates/_google_search.html

@@ -0,0 +1,17 @@
+        <h3>Site Search</h3>
+        <div class="google_search">
+          <script>
+            (function() {
+              var cx = '{{ GOOGLE_SEARCH }}';
+              var gcse = document.createElement('script');
+              gcse.type = 'text/javascript';
+              gcse.async = true;
+              gcse.src = (document.location.protocol == 'https:' ? 'https:' : 'http:') +
+                '//www.google.com/cse/cse.js?cx=' + cx;
+              var s = document.getElementsByTagName('script')[0];
+              s.parentNode.insertBefore(gcse, s);
+            })();
+          </script>
+          <gcse:search></gcse:search>
+        </div>
+