Build all 4 different boot_stage2 objects with SPI/2 and SPI/4 options.
Add a menu to the generic board to allow selecting between them.
Use the potato/4 boot2 for the Adafruit Feather until we have a better
version verified.
Fixes#42
Some paths hardcoded to my custom toolchain build dir, will be updated
to a package.json tools setup soon.
https://github.com/earlephilhower/pico-quick-toolchain
Blink and Fade examples work (i.e. digitalWrite/analogWrite/delay).
Includes a discovery script which will detect RPI Picos in UF2 bootmode.