[wpimath] Move math functionality into new wpimath library (#2629)

The wpimath library is a new library designed to separate the reusable math functionality
from the common utility library (wpiutil) and the hardware-dependent library (wpilibc/j).

Package names / include file names were NOT changed to minimize breakage.  In a future year
it would be good to revamp these for a more uniform user experience and to reduce the risk
of accidental naming conflicts.

While theoretically all of this functionality could be placed into wpiutil, several pieces
of this library (e.g. DARE) are very time-consuming to compile, so it's nice to avoid this
expense for users who only want cscore or ntcore.  It also allows for easy future separation
of build tasks vs number of workers on memory-constrained machines.

This moves the following functionality from wpiutil into wpimath:
- Eigen
- ejml
- Drake
- DARE
- wpiutil.math package (Matrix etc)
- units

And the following functionality from wpilibc/j into wpimath:
- Geometry
- Kinematics
- Spline
- Trajectory
- LinearFilter
- MedianFilter
- Feed-forward controllers

wpimath/src/main/native/include/units/force.h

@@ -0,0 +1,65 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2020 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+// Copyright (c) 2016 Nic Holthaus
+//
+// The MIT License (MIT)
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#pragma once
+
+#include "units/acceleration.h"
+#include "units/base.h"
+#include "units/length.h"
+#include "units/mass.h"
+#include "units/time.h"
+
+namespace units {
+/**
+ * @namespace units::force
+ * @brief namespace for unit types and containers representing force values
+ * @details The SI unit for force is `newtons`, and the corresponding
+ *          `base_unit` category is `force_unit`.
+ * @anchor forceContainers
+ * @sa See unit_t for more information on unit type containers.
+ */
+#if !defined(DISABLE_PREDEFINED_UNITS) || defined(ENABLE_PREDEFINED_FORCE_UNITS)
+UNIT_ADD_WITH_METRIC_PREFIXES(force, newton, newtons, N,
+                              unit<std::ratio<1>, units::category::force_unit>)
+UNIT_ADD(
+    force, pound, pounds, lbf,
+    compound_unit<mass::slug, length::foot, inverse<squared<time::seconds>>>)
+UNIT_ADD(force, dyne, dynes, dyn, unit<std::ratio<1, 100000>, newtons>)
+UNIT_ADD(force, kilopond, kiloponds, kp,
+         compound_unit<acceleration::standard_gravity, mass::kilograms>)
+UNIT_ADD(
+    force, poundal, poundals, pdl,
+    compound_unit<mass::pound, length::foot, inverse<squared<time::seconds>>>)
+
+UNIT_ADD_CATEGORY_TRAIT(force)
+#endif
+
+using force::newton_t;
+using force::newtons;
+}  // namespace units