Update readme.txt
Use Force60Hz=true
Synchronize audio subsystem with gcw0 build

  1. Implemented 3 backends: sdl mutex, sdl and libao
  2. New options --sound-sdl, --sound-sdl-old and --sound-ao
  3. New samplerates: 11025, 16000, 22050, 32000, 44100
A68k: Silence warnings for nasm 2.10.09 (labels without semicolon)
Add working a68k-mips core and enable it by default.