Pull from testing branch closes #31

* Needed to use a Liquid Tag block instead of a liquid tag,
  https://github.com/Shopify/liquid/wiki/Liquid-for-Programmers
  This allows the page.url to be parsed by liquid and passed to a tag.
* Needed to remove spaces around the tag.  Should probably handle this
  in the plugin directly.
added note about page
notebook excerpts improved on lab-notebook.html, and shows pageviews via google analytics #31
Computing analytics for every page on compile is a bit too ridiculously demanding.  Should compile with cron-job though or this method will not be dynamic enough