Serialize delta from tracks

[PerryRylance]

I don't think this applies to deserialization since this library is not concerned with deserializing real time streams.

Implementing serializing events without delta has presented some challenges when trying to plug in things like the microtonal event. Perhaps this needs to be typed as extending an array of events considering that it is. That would solve the issue with sendMessage.

More broadly, serializing delta on the track would save having to write special implementations for stream output, we could just send the events.