说明：  This tool is a simplification of the ballpivoting algorithm. It imagines a bella eating a delaunay traignulation in order to extract a manifold surface. It requires a single parameter: radius of the fretting ball. Ball Fretting Given a uniform sampled filled point cloud returns a tight triangulation. Input: ■tetr: a set of tetraedrons, nx4 array. If the cloud is not tesselated yet you need to call a delaunay triangulator prior calling this function. ■p : nx3 array, 3D set of points. ■r : the only parameter of the algorithm, the radius of the fretting ball Output: ■t : triangles ids, nx3 array ■tnorm: normals of triangles with outwards orientation