Refactor all the things

![x-all-the-things-template](https://cloud.githubusercontent.com/assets/1420926/2663008/846e8568-c04c-11e3-9e20-daffbcfe3f32.png)

Mainly refactored the code in Cornerstone to be more expandable in the future. Check out the highlights:

* Created `_variables.scss` file
   * Use the variables file to configure the various modules
   * The color palette is a spiffy Sass map
* Created `_type.scss` file
   * Obviously, define the type stuff
* Changed a lot of sizes and fonts for the eyebrow
   * Brand is way bigger
   * Nav list items are sans-serif font
   * The entire eyebrow module builds based on the values in the variables file
* Functions!
   * Added a function: `get-color(name, tone)` - Get a color from the palette based on the base name and color tone you're interested in
* Font Awesome
   * Included Font Awesome into the `<head>`
   * Added `fa-github-alt` icon to the GitHub button in the eyebrow