Split the two command implementations into separate libraries (#2012)

This will allow us at the user code side to determine to include old commands, new commands or both.

wpilibNewCommands/src/main/native/include/frc2/command/PIDSubsystem.h

@@ -0,0 +1,73 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 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 "frc/controller/PIDController.h"
+#include "frc2/command/SubsystemBase.h"
+
+namespace frc2 {
+/**
+ * A subsystem that uses a PIDController to control an output.  The controller
+ * is run synchronously from the subsystem's periodic() method.
+ *
+ * @see PIDController
+ */
+class PIDSubsystem : public SubsystemBase {
+ public:
+  /**
+   * Creates a new PIDSubsystem.
+   *
+   * @param controller the PIDController to use
+   */
+  explicit PIDSubsystem(PIDController controller);
+
+  void Periodic() override;
+
+  /**
+   * Uses the output from the PIDController.
+   *
+   * @param output the output of the PIDController
+   */
+  virtual void UseOutput(double output) = 0;
+
+  /**
+   * Returns the reference (setpoint) used by the PIDController.
+   *
+   * @return the reference (setpoint) to be used by the controller
+   */
+  virtual double GetSetpoint() = 0;
+
+  /**
+   * Returns the measurement of the process variable used by the PIDController.
+   *
+   * @return the measurement of the process variable
+   */
+  virtual double GetMeasurement() = 0;
+
+  /**
+   * Enables the PID control.  Resets the controller.
+   */
+  virtual void Enable();
+
+  /**
+   * Disables the PID control.  Sets output to zero.
+   */
+  virtual void Disable();
+
+  /**
+   * Returns the PIDController.
+   *
+   * @return The controller.
+   */
+  PIDController& GetController();
+
+ protected:
+  PIDController m_controller;
+  bool m_enabled;
+};
+}  // namespace frc2