Gets currently playing song path and saves it to one of 3 playlists. Comes very handy when it's made a shortcut in the wm's panel.
Requires infopipe.
Reentrant.
Usage: /bm [0|1|2].
Creates files /bm.lock, /bm0.m3u, /bm1.m3u, /bm2.m3u.
Playlists must end with newline. Does not correctly handle diactritic letters.