Add MegaCoreX support

[TheMasterFX]

Add MegaCoreX (official megaavr should work too but not tested). But MegaCoreX supports all new atmega devices so I chose that one. Tested on ATmega4808 and ATmega4809. It is mainly because of the new microsecondsToClockCycles implementation of megacorex and megaavr support and the Port Registers differ from atmega/tiny. This might change in the future