Consuming feeds

# Consuming feeds

It is great that the feeds package makes generating atom and rss feeds easy. But there are times where you want to consume. I've searched for other libraries that support consumming atom or rss, but none really exist in the Go-o-sphere. So I thought to create a small spike to see how much work it would be. Since most xml meta data is already set it should be quite easy to implement.

# what I did

* Added the missing xml meta data to a few typed child entities
* Added the `DownloadAtomFeed` and `ParseAtomFeed` methods
* Added tests to make sure it is working as expected
* I only touched the atom code

# what is next

* Not all meta data is added
* Atom Link entity in feed and entry have a single relation and should be a list [according to the specs](http://tools.ietf.org/html/rfc4287#section-4.2.7)
* Investigate the rss feed

Before I continue with my work I would like to discuss if this feature is inline with the pictured roadmap and if so, that I'm on the right direction.