***************************************************************
* Arduino PID Library - Version 1.2.1
* by Brett Beauregard <[email protected]> brettbeauregard.com
*
* This Library is licensed under the MIT License
***************************************************************

 - For an ultra-detailed explanation of why the code is the way it is, please visit: 
   http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/

 - For function documentation see:  http://playground.arduino.cc/Code/PIDLibrary

See too:
 - Arduino PID AutoTune Library:
   https://github.com/br3ttb/Arduino-PID-AutoTune-Library

   http://brettbeauregard.com/blog/2012/01/arduino-pid-autotune-library/
   
   https://playground.arduino.cc/Code/PIDAutotuneLibrary/