Add pico_rgb_keypad_midi example.

[AndrewCapon]

Turns the rgb_keypad into a simple midi device where the pads send midi note ons and note offs.

The device should appear as a midi device on the computer called "RGB Keypad".

There is a bit of mess here as my vscode stuff has wormed it's way in, sorry.

[Gadgetoid]

Sorry for being distressingly late here, but if you want to get this rolling again you can rebase the vscode settings commit out of this with:

git rebase -i HEAD~3

And changing the relevant commit from "pick" to "drop".

Add the conflicted .vscode/settings.json and git rebase --continue.

Then force push the result up to your branch.

You'll probably want to clone this branch to a new directory to do this, specially if you have anything going on in your working copy of pimoroni-pico.

This all sounded simple until I tried to explain it.

[IOSAudio]

I have no memory of actually doing this code!

[AndrewCapon]

I have no memory of actually doing this code!

Whoops posted under the wrong account!

[Gadgetoid]

@thirdr now we - finally - have MIDI support in MicroPython, maybe it's worth cleaning this up and combining it with a MicroPython counterpoint? 🤔

If keypad also uses the IS37FL31 driver (https://github.com/pimoroni/pimoroni-pico/tree/main/drivers/is31fl3731), we might need to slap up some MicroPython bindings for this and Keybow.