Integration with midly for full MIDI message parsing / support using "Owned" message variants

[masonium]

Initial branch based on the discussion in #35 .

Docs are probably a little sparse; I wasn't sure what should be copied / re-worded vs. what isn't really necessary.

I went with OwnedLiveEvent and OwnedSystemCommand as anologues to the midly variants, but I'm definitely not wedded to those names. I do think it's better to have different names than simply e.g. LiveEvent; the user can differentiate with qualified paths (midly::LiveEvent vs. bevy_midi::LiveEvent) but that strikes me as clunky.

[BlackPhlox]

Nice! Looking good!
As mentioned, I added a debug custom message for OwnedLiveEvent when NoteOn, NoteOff & AfterTouch.
Also fixed a bug in the piano example.
Haven't had time to check the input and output example yet, but I'll do that next 👍

[BlackPhlox]

I noticed that in the piano example, the function display_press translated the keys to an absolute value instead of a relative one, so we should do this instead:

fn display_press(mut query: Query<(&mut Transform, &Key), With<PressedKey>>) {
    for (mut t, k) in &mut query {
        if t.translation.y == k.y_reset{
            t.translation.y += -0.05;
        }
    }
}

[BlackPhlox]

Suggested change

	// let pitch = data.message.msg[1];
	// let octave = pitch / 12;
	// let key = KEY_RANGE[pitch as usize % 12];
	// if data.message.is_note_on() {
	// debug!("NoteOn: {}{:?} - Raw: {:?}", key, octave, data.message.msg);
	// } else if data.message.is_note_off() {
	// debug!("NoteOff: {}{:?} - Raw: {:?}", key, octave, data.message.msg);
	// } else {
	// debug!("Other: {:?}", data.message.msg);
	// }

[BlackPhlox]

I noticed that in the piano example, the function display_press translated the keys to an absolute value instead of a relative one, so we should do this instead... #36 (comment)

Made a pr to your branch with some updates to the piano example along with the above-mentioned issue: masonium#1