/**

 * \addtogroup mobility Mobility

 *

 * The mobility support includes:

 *  - a set of mobility models which are used to track and maintain

 *    the "current" cartesian position and speed of an object.

 *

 *  - a "course change notifier" trace which can be used to register

 *    listeners to the course changes of a mobility model

 *

 * The mobility models themselves are:

 *   - ns3::ConstantPositionMobilityModel: a model which maintains a constant position

 *     until it is changed by the user.

 *

 *   - ns3::ConstantVelocityMobilityModel: a model which maintains a constant speed

 *     until it is changed by the user.

 *

 *   - ns3::HierarchicalMobilityModel: a model which calculates the current 

 *     absolute position from a "reference" (parent) mobility model

 *     and a "relative" (child) mobility model. This allows users to

 *     compose mobility models.

 *

 *   - ns3::RandomWalk2dMobilityModel: a 2d "brownian" motion mobility model

 *     where the bounds of the mobility area are a rectangle.

 *

 *   - ns3::RandomWaypointMobilityModel: a 3d random waypoint mobility model.

 *

 *   - ns3::RandomDirection2dMobilityModel: a 2d random direction mobility

 *     model where the bounds of the mobility are are a rectangle.

 *

 */