The PathFrame class stores data a path's interpolating spline position, 
tangent, and normal data.                                               

A coordinate frame is defined by                                        

   id (int): The ID of a path point.                                       
   point (list([float,float,float])): A 3D path point.                     
   normal (list([float,float,float])): The normal to the path point.       
   tangent (list([float,float,float])): The tangent to the path point.     

id
   Path frame id.

normal
   Path frame normal.

position
   Path frame position.

tangent
   Path frame tangent.