Roboclaw

This adds a driver for the roboclaw motor controller and updates the segway controller for the new state machine. The current status on the roboclaw driver is that it can set the duty cycle of each motor and read the encoder positions, which is all that I need currently. It has a lot more features that we can add in later. Soon I want to add a uorb topic for motor encoders since this is a new type of measurement that we should consider using for position estimation of ground vehicles.