Polish landing page links, hero, and hover effect

* Update copy in introduction
* Improve color of hover links
* Add color and animation to global nav hover

![landing-hovers](https://cloud.githubusercontent.com/assets/3300569/4972253/c8f69464-68a8-11e4-860c-d664918d84ee.gif)

Now that I'm looking at it, I'm not either. And I can adjust the margin.