Add support for 8Mhz CPU

[odewdney]

conditionally moved the rol statement out of the delay to meet timing constraint for 8Mhz

[DavidEGrayson]

Thanks! Your code is now part of version 3.2.0 of the library.

By the way, I was able to test your code on an A-Star 32U4 Micro (which normally runs at 16 MHz) by simply adding these lines to the top of the sketch:

#include <avr/power.h>
#define F_CPU 8000000

and adding this line in setup:

clock_prescale_set(clock_div_2);