read_smf (formats 0 and 1, format 2 best effort) and write_smf (format 1,
960 PPQ) with the model they read into: Note, CtrlEvent, CtrlKind and
Sequence, in ticks at 960 per quarter note. serde on the model types is
behind the `serde` feature.
Moved from soundcraft crates/midi at 17d3f007: smf.rs, sequence.rs, the
error type, the SMF tests and the Sequence tests. The editing operations
(quantize, transpose, ...) and the display names stay in SoundCraft. Adds
a test for the MAX_TRACKS limit, which had none.
