Version 2.5: Re-enabled diagonal reflection.  Moved into the bundle
             (so it doesn't require a PLaneT install).  Added some picture variables.
Rewrote a bunch of things for compatibility with 5.1.
Version 2.4: Added change-to-color and map3-image.  Cleaned up documentation.
Version 2.3: Renamed files from .ss to .rkt, so they work better with Racket.  
             Added map-image, build-image, name->color, and friends; re-fixed bug in rotate-cw and rotate-ccw.
Version 2.2: Fixed bug in rotate-cw and rotate-ccw; restored reflect-vert and reflect-horiz; added with-input-from-url.
Version 2.1: Added argument type-checking.  And reflection primitives are now present but produce error message, rather than being missing.
Version 2.0: now fully compatible with 2htdp/image and 2htdp/universe.  No pinholes; temporarily disabled reflection primitives.
Version 1.6: fixed same transparency bug for 4.2.4
Version 1.5: fixed same transparency bug for 4.2.3
Version 1.4: fixed transparency bug for 4.2.2
Version 1.3: initial release, for DrScheme 4.2.4
Version 1.2: initial release, for DrScheme 4.2.3
Version 1.1: initial release, for DrScheme 4.2.2
