add under-score '_' to the end of data member names in Obstacle class

in
 - Obstacle class
 - SquareObstacle class
 - MockObstacle class
add under-score '_' to the end of data member names in World class

in
 - World class
 - MockWorld class
add under-score '_' to the end of data member names in Geo::Line class
add under-score '_' to the end of data member names in Robot class
add under-score '_' to the end of data member names in Action class
add under-score '_' to the end of data member names in DistSensor class

in
 - VirtualDistSensor
 - MockDistSensor