This adds both a midi generator and a midi type 1 simulator.
While I would have preferred to use an existing tool for this, I found
that timidity++ does not emit pitch wheel events correctly, and I
don't know of another widely-distributed tool that does midi-to-midi
format conversion.
The c++ and python versions were co-developed. I wrote one to test the
other. There is more cleanup to do, but `roundtrip.cpp` produces a
valid type 0 midi file given a type 1 or type 0 midi file as input.
