Fr: configurable pedal polarity for MPESynthesizer

yesterday i learned that there’s no standard for sustain pedals - some send 127 when open and 0 when closed while others send 0 when open and 127 when closed. it would be really great to allow both types of pedals to work with an MPESynthesizer.

(also the fact that MPESynthesizer supports sustain pedals out of the box is awesome! i couldn’t find it documented anywhere specifically though, even just a single sentence in the docs would be great.)