Add simple cycle counting

[MacDue]

• Adds simple cycle count to each instruction.
• Adds cycleMethod parameter to mos6502::Run() :
  • when cycleMethod == INST_COUNT run will execute cycles instructions.
  • when cycleMethod == CYCLE_COUNT run will execute cycles cycles.
• Adds cycleCount reference parameter to mos6502::Run():
  • This allows the actual count to be managed externally (including resetting/altering).
  • It also allows the external count to be updated while instructions are executed (needed if the count is used within the memory buses).
  • Corrects mixed tabs/spaces.

I've added this functionally as it was required for my use case -- so may help others.