Reduced logo file size & improved spacing in nav.

# Changes
 - Removed some layer effects and made a tighter crop on the logo (allowing it to scale better on mobile, and reducing unnecessary padding on image). __Reduced file size from 236KB to 52KB.__

/cc @barryclark @weerd 

# Screenshot
![screen shot 2014-11-14 at 11 02 53 am](https://cloud.githubusercontent.com/assets/583202/5048753/cc4b4266-6bed-11e4-997a-eb8f37ef56a1.png)


intrigued by this whole `$base-spacing` variable :)