Log Message:
audio/fasttracker2: Updates to v1.31

Changes since v1.30

v1.31 - 28.08.2020
- The audio channel mixer is floating-point based now, for a theoretical
  precision improvement.
- Windows: The 32-bit version now has the same mixer as the 64-bit version
  (e.g. you can use >48kHz rates).
- Fixed an issue where the channel panning could overflow if pan was close to
  255 ($80) and you had a panning envelope going upwards.
- Fixed another issue with dithering in 16-bit audio output mode (d'oh)
- Dithering is now always enabled for 16-bit audio output mode, and the
  "dithering" checkbox has been removed from the config screen.
- Disk op.: When listing modules, only list .wav files if "Save as:" is
  set to "WAV".
- Fixed a misplaced pixel on the "Usable" mouse pointer type graphics =)
- Code cleanup (more sensible variable names in the audio mixer)