Atmega8 5295cf4d

These two patches add ATmega8 support to Bus Ninja, and also simplify the code by merging the `__AVR_ATmega168__` and `__AVR_ATmega328P__` cases opening the way to add `__AVR_ATmega88__` and `__AVR_ATmega48__` support in the future (which I do not have the hardware to test right now.)