waves visuals: fixed minor glitch in fast transitions between sessions
sequencer: fixed bug which caused audio playback to stop working after first playlist loop
sequencer: added --preview option, replacing previous commented code
trying to solve problem with occasional exceeded SC memory by introducing a sleep after freeing sounds. this change has had a verified effect on a small playlist (neuromancer ch1-3, miracle) with preview=5.
updated playlist
sequencer: more predictable memory consumption, by loading most things at start-up rather than during playback.