Support ember and backbone simultaneously

This changeset fixes #58.

I tried to base changes on comments already in the issue. If the config option is true for multiple frameworks and ember, the code now checks for a ```.ember``` extension on files in order to compile them for ember; otherwise, it compiles them to the default JavaScript. I pulled most of the compile code into a function so that the additional logic checks still looked clean. Hopefully the config option name is sensible. I couldn't think of anything better. I also ensured that files like ```file.ember.hamlbars``` will still be compiled in this scenario as well.

I added a test and all existing tests are still passing.