Add support for LED matrix addressed directly (with PWM support).

This includes TimerOne for an ISR that only gets used if you use
that matrix type.
Currently, this supports 7 levels of intensity and partially supports a
matrix that isn't 8x8.
Support for bi and tricolor matrix (directly addressed or via a shift
register) will come next.

To be clear, this allows using this excellent library with non adafruit
hardware. I don't want to take bread away from your mouths, I have 
the adafruit hardware too ;) but I found it interesting to write support for 
barebones 8x8 matrix LEDs with direct addressing.