Add missing OctaMED effects 1D and 1E

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Reset MED synth volume slide on new note

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Refactor MED synth command interpreter

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

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Update med synth reference data

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