MIDI-Merger rev0

The first release, including firmware for a Raspberry pi Pico, and a PCB design (around that).

Supports up to 8 MIDI inputs merged into a single output.

Release files include gerbers, bill of materials, and component positioning file, all as used to order boards from JLCPCB.

Further includes a .uf2 firmware build so you can hold the "bootsel" button on the pico while connecting it to a computer over USB, and then drag/drop the uf2 file onto the volume it shows up as.

At the time of publishing, I've not yet received the rev0 PCBs, so it's unverified. I've previously tested the firmware with just 3 inputs on a breadboard prototype though, and it appeared to work well.