Added XboxController class (#140)

Joystick and Gamepad functionality was separated into cleaner interfaces.

wpilibc/shared/src/GamepadBase.cpp

@@ -0,0 +1,12 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2016. 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "GamepadBase.h"
+
+using namespace frc;
+
+GamepadBase::GamepadBase(int port) : GenericHID(port) {}