Support for Octopress feed aggregator pages and meta-feeds

A plugin and some supplement layout files that implement turnkey support for creating feed aggregator pages, and atom format meta-feed.

An example feed aggregator is here:
http://htcondor.github.com/planet

The equivalent meta-feed is here:
http://htcondor.github.com/planet/atom.xml

Blog post about the use:
http://erikerlandson.github.com/blog/2012/10/05/hosting-a-blog-feed-aggregator-with-octopress/