[hardware port request] STM32F4 Series

[Hyratel]

I was hoping to run this through a more-powerful STM32F4 Blackpill board (well, clone), but compile fails due to hard-include of AVR Watchdog Timer (not conditional on AVR-based board being used)

And then fails due to a namespace collision (CRC::) with the STM32 boardlibs

resolved to a successful compile by renaming CRC:: in the project to CRCFFB::

Have not live-tested on STM32F4 hardware

[njz3]

I did not try to compile myself on a STM32, but it should not be difficult to adapt the Arduino code to the platform.