SPI Speedup Trick Implemented

Program now tracks current value written to MOSI line before writing a
new value, reducing unnecessary writes to the MOSI line. Up to 25%
faster than current version when bits being written are mostly the same
(ex 00000000 or 11111111).  Otherwise, speedup is about 10% for most
data.
See SPI_Scope/SPI_Speedup for images of before and after.