Alternative navigation styling

As discussed in #26, here is an alternative idea for the top links. Since we're moving on from just a single link, I don't think it makes sense to continue with the button pattern. This pull basically adds a traditional navbar with 3 links (removing the GitHub banner in favor of the extra nav item). If we go with this, the nav labels can be renamed as you guys think makes sense.

Screenshot
![screen shot 2013-10-03 at 2 33 04 pm](https://f.cloud.github.com/assets/6104/1264405/8072e28c-2c5f-11e3-9ccd-e0437d60db05.png)

/cc @ben @vmg