#75 Support for MIDI keyboard as selectable input device

[Kizul Emeraldfire]

For those of us that have an MIDI keyboard, and want to play the Miracle Piano Teaching System game (which would be myself, among others), it would be awesome if NESTopia could use an MIDI keyboard for a 'controller'. :)

The M.P.T.S. keyboard option would probably also have to be added to the Input configuration, too, so that people could select which MIDI-In port they wanted/needed to use.