Split RobotDrive class into a class for each drive type (#552)

DiffDrive.CurvatureDrive (aka CheesyDrive) and KilloughDrive were also added.
This reorganization paves the way for SwerveDrive.

wpilibc/src/main/native/include/Drive/Vector2d.h

@@ -0,0 +1,28 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2017 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
+
+namespace frc {
+
+/**
+ * This is a 2D vector struct that supports basic vector operations.
+ */
+struct Vector2d {
+  Vector2d() = default;
+  Vector2d(double x, double y);
+
+  void Rotate(double angle);
+  double Dot(const Vector2d& vec) const;
+  double Magnitude() const;
+  double ScalarProject(const Vector2d& vec) const;
+
+  double x = 0.0;
+  double y = 0.0;
+};
+
+}  // namespace frc