Support for Raspberry Pi Pico

[oliverschmidt]

Certainly nothing to just merge as-is. Rather meant as a link to where it is located.

This PR adds support for emulation of the Apple2Pi card v6.x using the Raspberry Pi Pico - see https://github.com/a2retrosystems/A2retroNET

The Raspberry Pi Pico is connected to the Linux computer via its USB port, so every Linux computer with USB 1.1 ACM CDC virtual serial port (usually exposed as /dev/ttyACM0) support can be used.

For the Apple2Pi card v6.x see https://youtu.be/WHq4d5E-5p8?t=1083