Basic support for Gfycat

While Gfycat does have an oembed endpoint
http://gfycat.com/cajax/oembed/:id it doesn't return any information,
just an iframe in the html element
http://www.reddit.com/r/gfycat/comments/2kq4da/bug_gfycats_oembed_does_not_work_at_all/

I hope to someday rewrite this provider to use http://gfycat.com/api to
prove some more useful information and tighter integration.
Mention Gfycat on the list of providers.
Add AV Club
Merge pull request #46 from brycied00d/gfycat

Basic support for Gfycat