AVR timing calculation fix

AVR timer calculation fix, #6

SAMD21 timing fix

SAMD21 timing fix by @svlPanelMaker - #5

Add ESP32 compatibility

Uses same system as ESP8266

Added ESP8266 and SAMD21 (experimental) support

• Added ESP8266 support
• Added SAMD21 experimental support
• Has code for SAMD51, but I need a board to test and debug it.

SAM compatibility (Arduino Due)

• Added SAM (Arduino DUE) compatibility
• Some timing fixes
• Examples more correct (added volatile to variable used in ISR)

Code improvements

• Using static and instance and get rid of ugly global interrupt function
• Change public variables to private ones.

Add STM32 compatibility

• Add STM32 compatibility. Tested: AVR and STM32.
• Complete (ugly) rework of some private class members to public ones and interruption function to avoid STM32 hangs and errors.

AVR support

Still in development, but fully functional in AVR microcontrollers