Register support for post formats so plugins can make use of it.

This commit simply registers support for [WordPress post formats](http://codex.wordpress.org/Post_Formats) in the theme. Nothing particular fancy has to happen other than registering this support so that plugins (like [Tumblr Crosspostr](https://wordpress.org/plugins/tumblr-crosspostr/)) can recognize and make use of the format. I'm already using this on my site without issue.