Build process using GruntJS

As asked for in #26, this is a build process using GruntJS.

This guide will get you started: http://24ways.org/2013/grunt-is-not-weird-and-hard/

I'm using (grunt-yui-compressor)[https://github.com/mathiasbynens/grunt-yui-compressor] since your current build script also uses it, but the resulting files differ (probably because the Grunt task doesn't support all options). I'm only assuming the end result works, so please verify.