Feature homepage

Here it is!  I posted the mockups a few weeks ago, which pretty much exactly represent how the design ended up.  Here is a link to the mockup:

http://cl.ly/image/1p3T2A1b422C

There are some dynamic elements right now:

- The news feed section starts out with three default posts (in case something breaks, this is the fallback). It then grabs the API for the 20 most recent items and starts rotating them in.
- The issues, obviously, are dynamic. It pulls "beginner" issues from Github.
- It's not dynamic, but the avatars next to the discussion bubbles "tada" when you hover over the bubble... Just makes it feel more interactive.

There are some more things to do for the homepage, but I wanted to get this first version in and see how it works. The major TODOs are:

- Make it not suck on mobile. This might be a good beginner/intermediate task, because the layout is pretty easy for mobile
- Add in some section that talks about the philosophical ideals behind Pullup - mainly that it's an experiment and we're all just trying things out and seeing what we can build.  See @treygriffith's comment here: http://pullup.io/news/537cb3ea32ef5b04001b08b0