update 24 Dec 2014

Added:

cswirl.r and swirl.r — two functions to “swirl” an image.
cswirl does interpolation and thus runs longer; swirl just grabs the
nearest valid grid point.

slope text  plots specified text at specified locations along any
defined curve, AND plots the text rotated to match the local slope of
the curve.

wiggle is like swirl, but puts a lateral displacement whose magnitude
varies sinusoidally along the image