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)

`0`s before decimals

`0.2` or below: `0.15s` instead of `.15s`