NF: SoundPyo looping, parallels SoundPygame looping

- pyo internal looping is none or forever
- handle loop count by terminating after clip duration * loop count
  pros: simple, effective, smooth loop transitions (b/c in pyo)
  con: not sample-accurate end time (probably several ms off, not tested)
     this could mean that the offset is no longer apodized
- issue: apodized sounds can have a quiet dip at the loop point
- don't want a pyo _onEOS callback even if its possible (which is doubtful)