added binpacking functionality

Added new functionality using the binpacking npm library. 

Example Sprite:
![example_sprite](https://f.cloud.github.com/assets/187176/1800946/c2a1680a-6bd8-11e3-9454-e67a8e18e23f.png)
containing different famfamfam icons and pyconic-free

this method reduces the wasted "white space" to a minimum

ps: package.json is generated from npm by using npm install --save binpacking