Rewrite to fix shortcomings of previous architecture

[patrickberkeley]

Primary changes to the public interface that drove this rewrite:

• Require macro to either be keydown or keyup. This cleans up a lot of code where we were needing to determine whether or not the up/down event should be fired.
• Separate execution and modifier keys. Again this cleans things up a lot because we don't need to do a bunch of extra work to determine which keys are modifiers and which is an execution key. This also fixes #19 where it wasn't possible to fire a keyup macro's callback with a modifier key.

Other wins:

• Removes jquery dependency
• More thorough tests

[patrickberkeley]

@jordpo feedback implemented, ready for another 👁