dsound plays better
audio: new api
close audio before open. fix openal device not closed warning. issue 225
al, sl: wrong while condition. check processed > 0
sl: build error.wrong processed value. remove old code
ao: remove old code
ao: initialize al processed value. use timer to reduce error

fix al, sl crash on android
al on osx error ~ 1s/h
ao: split audio data with the size of audio output's buffer size
ao: api rename & add

Features not implemented
ao: reset internal states on open
ao: comments. add an audio playback example
Merge pull request #257 from wang-bin/ao

ao