keep refactoring the code

demo/ball_bounces.py

demo/ball_bounces_dev.py

demo/controller/example_controller1.py

demo/controller/example_controller10.py

demo/controller/example_controller2.py

demo/controller/example_controller3.py

demo/controller/example_controller4.py

demo/controller/example_controller5.py

demo/controller/example_controller6.py

demo/controller/example_controller7.py

demo/controller/example_controller8.py

demo/controller/example_controller9.py

demo/controller/example_two_car_sign_lane_switch.py

demo/demo1.py

demo/demo10.py

demo/demo2.py

demo/demo3.py

demo/demo4.py

demo/demo5.py

demo/demo6.py