Re: (iOS)Why use AudioQueue instead of AudioUnit

I think audio module on iOS has fault. In general, app opens playback at
startup, and works all time when app are runing. That is to say,
outputCallback in SDL_coreaudio.m will be called even if no sound require to
play. It will result to extra power consumption.

In previous version that using AudioUnit, I call AudioOutputUnitStop when no
sound require to play. When requiring, call AudioOutputUnitStart. This
method can avoid extra power consumption.

SDL2.0.5 use AudioQueue, it seems to be new way to avoid this problem.