Update PID loop to use only proportional/derivatives terms.  Update GPIO
bug.  Added "stop" executable to halt PWM process if it's stopped during
on state.

Changes to be committed:
	modified:   debug.h
	modified:   gpio.h
	modified:   main.c
	modified:   pid.c
	modified:   pid.h
	modified:   pwm.c
	new file:   stop
	modified:   therm.c
	modified:   types.h