TJAPlayer3 implementation details
(https://github.com/IepIweidieng/TJAPlayer3/blob/gh-pages/tja.md#senotechange):
- `#SENOTECHANGE` can be placed at the start of a measure, or in the
middle of the measure
- It will only apply to 1 note immediately after the command
- It will override any automatic Don2/Don3/Ka2 assignment (from note
clusters)
How it works in `tja2fumen`:
- `#SENOTECHANGE` will be tracked in the TJA measure object
- It will split the measure into sub-measures (similar to gogo/bpm/etc.)
- It will only be applied to the first note, after which it will be
overwritten
- We set a `manually_set` flag to ensure that the manually-chosen value
doesn't get overwritten.
Fixes#69.
85ea4d6efc