Add new (stubbed) API that simplifies use of the joystick library.

Joystick.cpp

@@ -19,6 +19,18 @@ void Joystick::Init() {
   if (_debug) Serial.println("DEBUG: Joystick library initialized.");
 }
 
+void Joystick::AddButton(uint8_t pin, ButtonType type) {
+  // stub
+}
+
+void Joystick::AddAxis(uint8_t pin) {
+  // stub
+}
+
+void Joystick::Update() {
+  // stub
+}
+
 void Joystick::SetAxis(uint8_t axis, int16_t value) {
   if (axis >= JOYSTICK_NUM_AXES) return;
   _joyReport.axis[axis] = value;