(Subjective) enhancements to how MMods work internally

[tertu-m]

Code for calculating the read BPM for MMods moved from Player to Steps and Trail
Lua functions for getting the read BPM for a Steps and Trail and the current read BPM of a PlayerState
The possibility of MMods being calculated for each chart rather than each song (not currently enabled)

[natano]

@tertu-m Do you have a use case for exposing the new functions to Lua?

[tertu-m]

If themes use GetMModReadBpm, they can know exactly what read BPM the MMod code will use to calculate the effective scroll rate. This means that themes don't have to duplicate the MMod code if they want to display the effective MMod speeds, and means if the way that ITGmania were to calculate MMods changed, themes would still be able to display accurate MMod values (switching from per-Song to per-Steps read BPM calculation being one example).

[tertu-m]

Sorry, I didn't clarify that was a use case. I've worked a StepMania theme that does that, and in theory Simply Love could use these calls to implement an MMod range on the options select screen.