wpilibc: Add overloads for units (#1815)

Add unit-taking overloads to the following classes:
- IterativeRobotBase
- LinearFilter
- Notifier
- TimedRobot
- Timer (HasPeriodPassed only)
- frc2::PIDController

The corresponding non-units-taking functions have been deprecated.

The return value of TimedRobot::GetPeriod() was updated.
This is a breaking change, users should use to<double> to get the value in seconds.

Other return values, e.g. Timer::Get(), have NOT been updated due to much wider use.

wpilibc/src/main/native/include/frc/IterativeRobotBase.h

@@ -1,5 +1,5 @@
 /*----------------------------------------------------------------------------*/
-/* Copyright (c) 2017-2018 FIRST. All Rights Reserved.                        */
+/* Copyright (c) 2017-2019 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.                                                               */
@@ -7,6 +7,9 @@
 
 #pragma once
 
+#include <units/units.h>
+#include <wpi/deprecated.h>
+
 #include "frc/RobotBase.h"
 #include "frc/Watchdog.h"
 
@@ -141,8 +144,16 @@ class IterativeRobotBase : public RobotBase {
    *
    * @param period Period in seconds.
    */
+  WPI_DEPRECATED("Use ctor with unit-safety instead.")
   explicit IterativeRobotBase(double period);
 
+  /**
+   * Constructor for IterativeRobotBase.
+   *
+   * @param period Period.
+   */
+  explicit IterativeRobotBase(units::second_t period);
+
   virtual ~IterativeRobotBase() = default;
 
   IterativeRobotBase(IterativeRobotBase&&) = default;