Stage 2 (before final 0.2.0):

* timer interface (done)
* sequencer (first pre-alpha exist)
  - only external MIDI support

Stage 3:

* sequencer
  - add internal synthesizer interface (envelopes exist)

Stage 4:

* sequencer
  - add MIDI emulation for internal synthesizer

General:

* check why S3 SonicVibes volume levels are non-linear
* debug ES1371 code (with external testers)
* add MIC gain switch for CS4231 (without InterWave?, AD1848 too?)
* add PCM switch for ADC overrange setup - CS4231
* add CTL switch Game Speed Compensation (GUS, SonicVibes)
* add CTL switch Joystick Enable (GUS, AudioPCI)

* extend documentation for programmers (driver side)
* extend documentation for users
* detection for OAK Mozart soundcards
* detection for Yamaha OPL3-SA[2,3] soundcards
* code for multiple playback PCM devices for GF1 chip (GUS cards)
