implement timestretch in audiocommon

This is half c&p from OpenAL backend using soundtouch, so this library will stay in dependency for ever :-)
This should also fix the 1h30 bug as the buffer handling is rewritten: http://forums.dolphin-emu.org/Thread-the-1h30-audio-issue-mystery

thx @ moosehunter for all the debuging on the 1h30 bug. He did much more than me
fix android build
time stretch: decrease latency