Delaunay Triangulation and Dirichlet (Voronoi) Tessellation
Calculates the Delaunay triangulation and the Dirichlet
	or Voronoi tessellation (with respect to the entire plane) of
	a planar point set. Plots triangulations and tessellations in
	various ways.  Clips tessellations to sub-windows. Calculates
	perimeters of tessellations.  Summarises information about
	the tiles of the tessellation.	Calculates the centroidal
	Voronoi (Dirichlet) tessellation using Lloyd's algorithm.