New perspective plot functions for points, lines, etc. on a surface.

   plot.im.R
   persp.im.R [New file]
   perspPoints.Rd [New file]
        Split off persp.im to a separate file.
	New functions perspPoints, perspLines, perspSegments, perspContour
	for plotting things on a surface.

   NEWS
   DESCRIPTION
   updates.Rnw
	updated.