Launchpad Mini details of interest in firmware source

I found some interesting details in released firmware source for the Launchpad S that works fine on my Launchpad Mini, and I reference them here to make the information more widely available.  See the [MIDI message handler in midi.c](https://github.com/Focusrite-Novation/launchpad-firmware/blob/master/main/midi.c).