Increased possible servo count

A small optimization shaved off a few cycles in the pwm handler.

Also, most libraries I could find online has a resolution of 60 for servo
signals. I've reduced the resolution to 128 allowing us to now have up to
31 pwm signals simultaneously.
Made several small changes

Standardized the use of tCallback where applicable, and sanitized the
return value of GetPin
Improved timer module

1. Added the ability to use ints as identifiers for functions, allowing
you to stop currently registered functions.

2. Fixed a lot of bugs that I didn't notice. Should have tested better.
Mostly related to not getting accurate time. One was a missing volatile
adjective. Underflow issue. Race conditions.