[PCB] Test v2.0 and improve v2.1 boards

[SmittyHalibut]

Receive prototypes from #63 and test. Find any changes needed.

Also: Add any additional feature requests here:

• Current limiting/fusing on GPIO and SAO headers power pins
• Pull-ups on I2C bus. Oops.
• ADD MORE HERE (or, if you can't edit, just post to this ticket.)

[SmittyHalibut]

Received boards from JLCPCB! On to testing.