Tighten up the navigation

Fixes:
Broken hover on the navigation.
Fixed spacing 

Additions:
Improved the scaling on the header:
!['scalingdemo'](http://i.imgur.com/UsCKoDM.gif)


Improved spacing and added hover states to the navigation on /learn.html
This is prep work for the possibility of using something like affix.js (http://getbootstrap.com/javascript/#affix)
so it's easier to navigate the API.
!['siderbar'](http://i.imgur.com/N5Ft3mI.png)