Merged two "ifs" into one

[madacol]

Merged this two ifs:
if(!pOnE) outputSum-= kp * dInput;

if(pOnE) output = kp * error;
else output = 0;

into this one:

if(pOnE) output = kp * error;
else { outputSum -= kp * dInput; output = 0; }

I expect a performance improvement by the if reduction, or am I missing something?

I also separated the derivative computing from the ouputSum merging to add comments to indicate where each parameter is being computed.

Changed this:

      /*Compute Rest of PID Output*/
      output += outputSum - kd * dInput;

into this:

      /*Compute derivative*/
      output -= kd * dInput;
      /*Merge*/
      output += outputSum;

I believe it will compile the same, whether is separated or not. But if you don't like this part I'll remake the PR to remove this.