Support playback from MIDI format

[ritiek]

It might be possible to use rimd crate to parse .mid files and play them in piano-rs.

Basic rimd usage that could be handy to us:

extern crate rimd;

use rimd::SMF;
use std::path::Path;

let midi = SMF::from_file(Path::new("/path/to/example.mid")).unwrap();
for track in &midi.tracks {
    for k in &track.events {
        println!("{:?}", k);
    }
}