GCW0: Move sound code to separate files. Add new samplerates.

  snd.cpp - now contains general data and audio driver choosing
    sdlaudio.cpp - SDL audio backend
    aoaudio - libao audio backend

  Now use --sound-ao for libao backend and --sound-sdl for SDL.

  New samplerates: 11025, 16000, 22050, 32000, 44100;
  16000 and 32000 seem to be the best for 60hz synchronizing.