Implemented synchronous PID controller (#993)

SynchronousPID provides a Calculate() function for teams to call themselves
instead of running the controller with a Notifier.

wpilibc/src/main/native/include/SynchronousPID.h

@@ -0,0 +1,33 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include "PIDBase.h"
+
+namespace frc {
+
+/**
+ * Class implements a synchronous PID control loop.
+ *
+ * Provides a calculate method for the user to call at their desired update
+ * rate.
+ */
+class SynchronousPID : public PIDBase {
+ public:
+  SynchronousPID(double Kp, double Ki, double Kd, PIDSource& source,
+                 PIDOutput& output);
+  SynchronousPID(double Kp, double Ki, double Kd, double Kf, PIDSource& source,
+                 PIDOutput& output);
+
+  SynchronousPID(const SynchronousPID&) = delete;
+  SynchronousPID& operator=(const SynchronousPID) = delete;
+
+  void Calculate() override;
+};
+
+}  // namespace frc