Add first pass at Ember guidelines

These are the first few things I've seen that are consistently useful. All feedback and input is appreciated.

cc: @jsteiner @BlakeWilliams @seanpdoyle @halogenandtoast @creuter @MattMSumner @JoelQ 
@gabebw that was my thoughts and I why I went this way.

I do think that keeping this guideline using `this` would make sense as the Ember team is pushing ES6 and may not support coffeescript in the future.