remove some unnecessary files; clean up code

.gitignore

demo/ball_bounces.py

demo/demo1.py

demo/demo10.py

demo/demo2.py

demo/demo3.py

demo/demo4.py

demo/demo5.py

demo/demo6.py

demo/demo7.py

demo/demo8.py

demo/example_two_car_sign_lane_switch.py

demo/plot2.py

demo/plot_test.py

demo/plot_test1.py

dist/dryvr_plus_plus-0.1-py3.8.egg

dryvr_plus_plus/plotter/plotter2D.py

dryvr_plus_plus/plotter/plotter2D_new.py