libmpg123 is more "loud" than libmad, at least for the mp3s that I have around. Is also newer and maintained. I've heard is also faster, but amused is so simple that it doesn't make any difference.

now it includes all the params, not only the rate

otherwise we keep garbage in the playing queue.

IMSG_ERR needs a playlist_dropcurrent(), but otherwise is just the same as IMSG_EOF: the current song ended and we need to move forward. To unify, set current_song to NULL in playlist_dropcurrent, which make sense since right after it we're not playing anything.

this avoids the player skipping two songs on failure.

was useful for debugging but now ther's the `status' command for it.

otherwise the output may get buffered by a pipe and it's not pretty.

this pings all the "interesting" events to clients that issued a IMSG_CTL_MONITOR, except to the one that generated such event.

libmad gives us sample at 32bps, but we scaled back to 16 because minimad.c does so. However, the scale producedure from minimad.c kinds of corrupts some audio files, they don't play well. We can leave the problem to sndio which solves it better than us.