Changes in OpenSL API and audioplayers handling

* Remove Destroy() from API
* Native audioplayers are automatically destroyed when application pauses, so no need to destroy them on client code.
Add a semaphore to PauseEvent
Add an explicit Destroy method to the audio player
Add dummy destroy method to sound_xorg.go
Merge branch 'master' of https://github.com/remogatto/gorgasm