Added BNDKVOTrigger.
Changed the responsibility of BNDBinding.

It now updates objects, but does not listen for KVO notifications. That is the role of BNDKVOTrigger.
BNDBinding is a composite for triggers.

[BNDBinding bind] calls startFiring on all triggers.
[BNDBinding unbind] calls stopFiring on all triggers.
Added documentation for all header files.