Clean start

Program Memory Usage  : 3048 bytes   74.4 % Full
Data Memory Usage   : 79 bytes   30.9 % Full
Time in Refresh (min/max): 153us/174us

Starting with very clean and readable, but non-optimized code.
Move lookup tables into SRAM
Cache PORD and PORTB values locally
Cache ColBits and lift them out of a conditional
Cosmetic code cleanup before merging into master