Rewrite into CoffeeScript

Just for the sake of it :smiley: Obviously it wasn't tested on any real-world application, and there are some minor code-by-code differences, but it does pass all the tests. :sparkles: 

Now that the code is here we can at least do some measurements to see what would be the performance and generated code-size differences. Some numbers will be great and I will look into putting some jsPerf snippets.

This is a toy, but if someone is interested in pushing it further and maintaining it for future versions of Backbone, I have a separate project [here][backbone.coffee]. There is also a docco [annotation][].

[backbone.coffee]: https://github.com/gsamokovarov/backbone.coffee
[annotation]: http://gsamokovarov.github.com/backbone.coffee/