Add sponsors block

Here's a pass at adding a block for the sponsor logos. I didn't really care for how wide the line length was for the "Planned features" section, so I thought putting the block to the right would help reduce that line length and would display the sponsors more visibly than at the bottom. For Ryan Durk, I just made a sort of generic logo image that fits in with the other.

![screen shot 2014-03-30 at 1 44 18 pm](https://cloud.githubusercontent.com/assets/6104/2561974/5236470a-b833-11e3-89db-2339bf7951f3.png)