feat!: implement vsti, along with various refactorings and api changes for it

The RPC and sync library mechanisms were removed for now; they never really worked and contained several obvious bugs. Need to consider if syncs are useful at all during the compose time, or just used during intro.

tracker/note_id.go

@@ -0,0 +1,19 @@
+package tracker
+
+// Describes a note triggered either a track or an instrument
+// If Go had union or Either types, this would be it, but in absence
+// those, this uses a boolean to define if the instrument is defined or the track
+type NoteID struct {
+	IsInstr bool
+	Instr   int
+	Track   int
+	Note    byte
+}
+
+func NoteIDInstr(instr int, note byte) NoteID {
+	return NoteID{IsInstr: true, Instr: instr, Note: note}
+}
+
+func NoteIDTrack(track int, note byte) NoteID {
+	return NoteID{IsInstr: false, Track: track, Note: note}
+}