Breakout — Milestone #4

For Milestone #4, you need to implement collisions between the ball and the objects on the window. The steps in this process are:

1. Design and implement a get_colliding_object function, as described in the handout.
2. As part of your step function for advancing the ball, call get_colliding_object to see whether the ball has hit anything. Remember to capture the result of this function call in a variable.
3. If the colliding object is the paddle, bounce the ball upward. If it is a brick, bounce the ball and remove the brick.