[test] Test more note slide effects

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Add test for note slide with retrig

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Fix note slide with retrig

PTM has a note slide effect which retrigs the instrument at each step.
We don't have a reference player for PTM files so we're assuming this
is the correct behavior (at least until someone reports a bug).

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Update changelog

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>