Robot to stay in center of hallway.

This updated program should force the robot to stay in the middle of the hallway. This is how the program works:

- Set up the sonar by placing the robot in the center of the hallway. This set up gets the distance to the left and right wall using the sonar. The robot cannot be moved during this time so that it can get a correct reading.
- After four seconds, the robot will begin to move. It'll probably go off track initially.
- Once the robot detects it's moved off track, a drift function is called. This function sets the speed of the motors, so it has full control of the robot. It loops until the sonar value for a particular side is no longer greater than the distance to that particular wall. This puts the robot back in the center of the hallway.