Fix volume computation in MED synth

MED synth instruments have their own volume, and volume changes in the
volume table won't affect normal channel volume.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Handle MED hold/decay event

MMD0/1/2/3 MED decay events are set as instrument numbers without notes.
The instrument note is the decay value for regular instruments or jumps
to the volume table for synth instruments.

This patch sets an FX_MED_DECAY effect for decay events, but actual
decay or JVS effect processing is left to a future patch.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Fix MMD effect handling

Handle arpeggio as pass-through and ignore hold and decay until properly
implemented.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Don't add test file into the library

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Update changelog

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>