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