Add new C++ Command framework (#1785)

This is the C++ version of #1682.

The old command framework is still available, but will be deprecated.

Due to name conflicts, the new framework is in the frc2 namespace.
Eventually (after the old command framework is removed in a future year)
it will be moved into the main frc namespace.

wpilibc/src/main/native/include/frc2/command/WaitCommand.h

@@ -0,0 +1,52 @@
+/*----------------------------------------------------------------------------*/
+/* 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 <memory>
+
+#include <wpi/Twine.h>
+
+#include "CommandBase.h"
+#include "CommandHelper.h"
+#include "frc/Timer.h"
+
+namespace frc2 {
+/**
+ * A command that does nothing but takes a specified amount of time to finish.
+ * Useful for CommandGroups.  Can also be subclassed to make a command with an
+ * internal timer.
+ */
+class WaitCommand : public CommandHelper<CommandBase, WaitCommand> {
+ public:
+  /**
+   * Creates a new WaitCommand.  This command will do nothing, and end after the
+   * specified duration.
+   *
+   * @param seconds the time to wait, in seconds
+   */
+  explicit WaitCommand(double seconds);
+
+  WaitCommand(WaitCommand&& other) = default;
+
+  WaitCommand(const WaitCommand& other) = default;
+
+  void Initialize() override;
+
+  void End(bool interrupted) override;
+
+  bool IsFinished() override;
+
+  bool RunsWhenDisabled() const override;
+
+ protected:
+  std::unique_ptr<frc::Timer> m_timer;
+
+ private:
+  double m_duration;
+};
+}  // namespace frc2