Zen check: Module should not have a dash in the file name.

[JAL-code]

• Replace car_main.py with carmain.py

classes/car_main.py

• Fix electric_car.py with updated reference to new carmain.py name.

classes/electric_car.py

from car_main import Car
to
from carmain import Car

• Ditto for example file:
  classes/my_cars_split_module.py

from car_main import Car
to
from carmain import Car