added multi-dimension vector class
Use new class style, fix one typo
update Point class with new style class
update 2D Point class with new style class
use inheritance to define Point2D to avoid code doubling.
Fix some syntax error in the Line class. There seems to be more .
There are serious problem with the Line class. Will fix later
Finished with Line class. Interaction with plane will be implemented in the future.
update Line and Point in Geometry