updated Package to 1.2.6 with all previous source updates:
* Updated Arduboy2 library to 5.2.1
* updated ATMlib to 1.2.6
* added support for LCD_ST7565 backlit displays
* Added Flash Chipselect options to tools menu
* optimized core wiring.h
* Enter bootloader mode button combo changed to pressing UP+DOWN for ~1,5 seconds
* updated Cathy3K bootloader