artf4127: Implemented velocity PID controller

Change-Id: I8c0f84422f7ca0ac5c50fddb282fb3452ee1d491

wpilibc/wpilibC++Devices/src/Encoder.cpp

@@ -475,17 +475,6 @@ int Encoder::GetSamplesToAverage() const {
   return result;
 }
 
-/**
- * Set which parameter of the encoder you are using as a process control
- * variable.
- *
- * @param pidSource An enum to select the parameter.
- */
-void Encoder::SetPIDSourceParameter(PIDSourceParameter pidSource) {
-  if (StatusIsFatal()) return;
-  m_pidSource = pidSource;
-}
-
 /**
  * Implement the PIDSource interface.
  *
@@ -493,10 +482,10 @@ void Encoder::SetPIDSourceParameter(PIDSourceParameter pidSource) {
  */
 double Encoder::PIDGet() const {
   if (StatusIsFatal()) return 0.0;
-  switch (m_pidSource) {
-    case kDistance:
+  switch (GetPIDSourceType()) {
+    case PIDSourceType::kDisplacement:
       return GetDistance();
-    case kRate:
+    case PIDSourceType::kRate:
       return GetRate();
     default:
       return 0.0;