Using all the work from @hfellner and others, add FreeRTOS
SMP support.
Allow idling cores through the FreeRTOS FIFO queue to
allow for file system and EEPROM support.
Make delay a weak function so FreeRTOS can override.
Add cycle count support under FreeRTOS using a PIO SM.
Use a task-based approach for handling the USB periodic work
instead of the IRQ-based one in the main core.
Set 8 prio levels so it fits in 3 bits nicely (0..7).
Fixes#171
Under Windows, it is very hard to make a symlink and by default git won't
make one to the Arduino API directory, causing annoying build errors.
Avoid the issue by duplicating the ArduinoAPI directory explicitly and using
CI to verify that there are no differences between the two.
Earle F. Philhower, III