Restyle package page, fix markup errors, remove duplicate CSS include

This PR restyles the package page. While I was doing that, I also fixed some HTML validation errors, and removed a double-include of the main.css stylesheet.

![screen shot 2014-12-14 at 8 55 32 pm](https://cloud.githubusercontent.com/assets/3019349/5431055/edb0536c-83d3-11e4-82a2-e82515046166.png)