Add AEAudioUnitFilter Bypass capability

This is a light-weight commit that adds the ability to keep a filter block inline and bypass it at any time. See open issue #12 for enhancement request.

Note that care is taken to make sure state-based effects (like reverb and delay) will clear out before being un-bypassed so there is no carry-over from previous sounds before the bypass was switched on. This occurs exactly once via `AudioUnitReset` on state change.