Add support for other MCU e.g SAM, ARM, ESP, etc

[mikaelpatel]

[joede]

That would be very interesting. May be libopencm3 could act as some kind of HAL.

[mikaelpatel]

See experimental multi-target Arduino libraries: https://github.com/mikaelpatel/Arduino-GPIO https://github.com/mikaelpatel/Arduino-SPI https://github.com/mikaelpatel/Arduino-TWI https://github.com/mikaelpatel/Arduino-OWI https://github.com/mikaelpatel/Arduino-Scheduler These may be used to refactor Cosa to support multi-target.