Make hardware cycle-counting

[Brandon Pitman]

All hardware should have cycle-counting functionality, and should be timed against the number of cycles that pass. High-level steps:

• CPU should track its own clock speed (constant for CPU, set at time of construction, in Hz)
• Hardware should have standard method to receive a number of cycles that have passed
• CPU should use this method each time step() is called
• Existing cycle-counting hardware should be moved over to this functionality
• CPU should have functionality for running for certain amount of "real time", calculate to cycles

[Brandon Pitman]

Implemented in 7c42db4.