fix copy-paste error with timerb registers.
add testbench for cia6526. Coverage is far from complete.
fix various bugs in CIA implementation that prevented effective
reading and writing of registers.
add debugging for CIA port access
try to fix CIA port reading bug that does not occur in the simulator.
Basically if DDR=in, set bits in the output value for that port would
mask zeros in the input.
try to allow serial monitor to receive back to back characters instead
of losing frame.
map HESMON monitor cartridge at $C000 by default for debugging.
refactoring
more work trying to get port reading to work on CIAs.
In simulation I can read input values easily, but once synthesised,
I have to set reg_portb_out to zeroes to read from reg_portb_ddr,
even through reg_portb_ddr is set to zeroes.  Weird.