Add unit tests

Hey @jayphelps. Nice project. I made a similar attempt at doing this a while back but I was unaware of `Ember.config.overrideAccessors` and my result wasn't as elegant as yours. Here is a set of unit tests I was using to guide my development. Of the 28 unit tests here 11 of them currently fail, however, with some work it should be possible to get them all passing.