- add 'chanset' in user.c and doc

- check (one by one) that every function works and
  that the documetation is accurate. Make a relsease.

- make song{play,record,idle} scan tracks for controllers,
  pitch bends, prog changes etc... so that the output
  will be in the same state as the song were played from the 
  beggining

- implement undo-stack

- make songplay stop after the EV_STOP is received or
  create a songperf or whatever. But we need songplay to
  stop in scripts such as smfplay(1).

- receiving 'EV_STOP' in slave-mode make all notes off; why?

- add curves in filt.c

