Intersection of a plane with an arbitrary surface data. The surface must be in the form of faces and vertices strcture such as patch function and the faces of the surface must be defined with triangles. fv =
faces: [number of faces x 3 double]
vertices: [number of vertices x 3 double]
"p0" and "n" is used to define the plane. "p0" is a point that lies on
the plane and "n" is the normal vector of the plane.
The function actually calculates intersection segments of triangels of
the surface with the plane and finally all the calculated segments is
linked to each other to form a continuous intersection region