Adds support for estop reading and horn actuating.
PDController's will now only run if the estop has the motors enabled.
A yellow light has been added to the shield that will indicate motor enabled/disabled status.
The car_interface node now listens for std_msgs::Bool messages on the /car_horn topic.
Writing true to this topic will turn the horn on. Writing false will turn the horn off.
Merge pull request #6 from barulicm/car-interface

Adds support for estop reading and horn actuating.