Commit Briefs
flush stdout after each monitor event
otherwise the output may get buffered by a pipe and it's not pretty.
add a monitor functionality
this pings all the "interesting" events to clients that issued a IMSG_CTL_MONITOR, except to the one that generated such event.
mp3: don't scale back to 16bps
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.