Adds the SetOutputSum(sum); function.

Add Reset() function to clears pTerm, iTerm, dTerm and outputSum values.

Resolves #65, #66 and #67
Thanks @drf5n

Also adds a new "toggle" controller mode that toggles between manual and automatic mode.

• Added default constructor

• Added default constructor

Updated SetTunings to clear outputSum variable if Ki parameter = 0.
Suggested by @brN2k, issue #48.

• Fix bug in overload constructor Thank you @guilhermgonzaga
• Updated PID_RelayOutput.ino example where now the PID compute rate controls the rate of updating the digital output (thanks to suggestion by @SinisterRj). Other features include debouncing all transitions, full window range control and only one call to digitalWrite() per transition. Use with controlling mechanical relays, SSRs, MOSFETs or other devices.

• Since ESP32 Arduino 2.0.1 or newer has analogWrite basic support based on LEDC, the included library ESP32-ESP32S2-AnalogWrite has been removed from QuickPID. Please Install SP32-ESP32S2-AnalogWrite separately if you require its advanced pin management or other unique features.

• Uses dispKp = 0, dispKi = 0 and dispKd = 0 for both display purposes and defaults. Removed defKp, defKi and defKd.

• Autotune_QuickPID.ino example is now at the sTune repository.