Removed the operators which mixed Millisecond and Microsecond. I decided that this should be explicit.

Added addition and subtraction operators.
I made pwm_parallel_writer compilable.
I rewrote the parallel reader to be more maintainable at the expense of more memory consumption. I decided I was prematurely optimizing. This class is far easier to comprehend and follows the writer implementation.
Added a utility which makes it easy to read and report a pwm value.
This will mostly be used for getting my the values reported by my transmitter.