Added build.js and edited Cakefile for building with local cake

With this change, you can build using local versions of cake and coffeescript like so:
    
    node build.js all
    node build.js watch

etc! If we like this, we can update the README accordingly. And you can still use a globally installed cake if you prefer (though it will call upon the locally installed coffeescript if available).

So all it takes is an `npm install` to setup build dependencies.