rewrite Crafty.unbind

see discussion at issue 417 --
https://github.com/craftyjs/Crafty/issues/417
add unit tests

Add tests to confirm Crafty.bind and Crafty.unbind behavior;
Add unit test for Crafty('*') [which currently fails, a known issue];
Force tests to run in order; they were not written atomically;
Add note to developers for how to run these tests conveniently.
Merge pull request #420 from sbyrnes321/unbind

rewrite Crafty.unbind