Support Haml through Calliope in View Layer

All that is needed is to start putting `*.haml` files in the templates folder and Calliope will pre-compile them into EEx strings. Actually, because of the way that it works you can mix and match Haml and EEx templates. 
I just tried creating a key myself and it worked. Please open an issue on hex or ping me on IRC and we'll continue the discussion there.