Add feature to fix desync from BPMCHANGE in songs previously converted by tja2bin

[vivaria]

In #64, I added the ability to run tja2fumen on .bin charts, fixing the don/ka types based on timing, for previously-converted bins that don't have the correct don/ka values.

In theory, I could take this further, for example by checking for BPM changes between measures and re-computing the offset values. This should fix desync caused by the old tja2bin, see: Fluto/TakoTako#16

I don't know whether this is wanted, though, so I will leave this for now unless someone specifically asks for it.