Initial testing of PID control

PID control ended up being very spastic, probably because of scaling factors. PID output was not scaled down, so the motors were being fed extraordinary values (including negative, which the Motor class interprets as "prime").

So, greatly scaled down the PID output before sending values to motors, and this showed that, consistently, the motors sped up on the opposite side than intended. So I added the negative of what was being added before. I can't rationalize why it is backwards, unless the calculated angles increase CW instead of CCW. (also depends on interpretation of gyroscope readings).

Haven't yet tested these most recent changes. Next steps are to try to tune the PID factors to match the system.
Merge branch 'master' of https://github.com/quadcopter5/quadcopter