remove more unneeded VST functions
instantiate LV2::Synth, not AudioEffectX
move keymap initialisation to separate function
replace VstInt32 with uint32_t
begin moving voice-related stuff to mdaPianoVoice
move shared definitions into mdaPianoCommon
remove program change handler
rename LV2::Synth parameters
move destructor into header, declare load_* functions
move mdaPiano::noteOn to mdaPianoVoice::on
create mdaPianoVoice objects
implement note reset
remove processReplacing

`processReplacing` is almost the same as `process`. The differences are
now in `process`, but commented until further review.
move `process` to voice
remove call to `suspend`
remove `resume` function
rewrite `processEvents` as `handle_midi`