Added calculation for dutyPos. Sound, but broken.

- Added/changed renderFrame code to add calculations for dutyPos and
Positive/Negative
- Added some basic IRQ code, but it is not ever called
- Audio still completely broken, only one channel (rect1) but not
working
- Fixed CPUCycles not being added for NMI.  It was being reset to 0 and
then returned instead of returning 7.
- Can get familiar sounds for many games (Galaga, Excitebike, SMB, many
others) if I set if(length < 0) to if(length >=0).
- Still broken