Feature: Add default sprite support.

## Ready State: Yes

This pull request adds a default sprite configuration for the theme and documentation to describe how to use sprites with compass. 

## Requirements & Dependencies

* This addition requires that a directory is created to house the individual sprite images: `/img/sprite`

## Usage/Test Instructions

* Add individual images to `/img/sprite`
* Run `compass compile`
* Utilize the generated css to apply sprited background images