Mainly convert mainloop and audio thread into native code for
performance increase. (Calling into JNI every frame was costy)
The code was cleaned up quite a bit, but I may have introduced new bugs
in this process :<
Former-commit-id: fdbc21b5ab39f3d2e36647fd1177dc9a84a16980
Former-commit-id: ac765dbee8c994e1b69cc694846511837c2685b9