Move the power switch pin to the other side of the pico for easier mounting
Disable the UART lines while in power-down mode

When the device is powered off but the UART is attached
the little bit of power from the UART line can keep
parts of the test device awake, making the next boot
act weird. This puts the UART pins in input mode
while in the poweroff state to prevent power leakage.
Fix the USB serial number
Update diagram URL
Add protocol documentation to the README
Default to 9600 baud like operating systems expect

The OS doesn't read the baudrate for the adapter ever, it ony assumes it's 9600 by default and writes new modes when required
Add slightly more documentation

The serial port handling functions are slightly confusing, added more docs
Fix passthrough on uart1
Initial commit