Update by James Courtier-Dutton <James@superbug.demon.co.uk>

Update by James Courtier-Dutton <James@superbug.demon.co.uk>

0.0.12
   Correct interrupt timing. interrupt at end of period,
   instead of in the middle of a playback period.
   Remove redundent "voice" handling.
0.0.13
   Single trigger call for multi channels.
0.0.14
   Set limits based on what the sound card hardware can do.
   playback periods_min=2, periods_max=8
   capture hw constraints require period_size = n * 64 bytes.
   playback hw constraints require period_size = n * 64 bytes.