midi-dump: exit cleanly, add support for absolute+relative timestamps

Signed-off-by: Robin Gareus <robin@gareus.org>
add usage() to jack_midi_dump

Signed-off-by: Robin Gareus <robin@gareus.org>
realtime-safe midi-dump (use ringbuffer)

Signed-off-by: Robin Gareus <robin@gareus.org>