Updated the sonar module prototype.
The biggest change to the proposed node is a restructuring of the sonar code style. Two services (sonar_toggle and sonar_set_scan) allow another node to turn the sonar on and off. The sonar constantly scans, keeps track of its position, and publishes all its readings in the topic sonar_direction.msg.
Added the appropriate message and service files, and the code skeleton.
The most obvious missing part of the code is the part which controls the movement of the sonar sensor, which should constantly scan between two ranges without user intervention.