Update error messages for image-select-x.
Update image-get-layer to handle new Mediascript model (lists instead of vectors in some cases)
Add point.rkt, an improved version of positions.rkt.
Minor update to comments on 'string-contains?'
Add draft of macro alternative for error/parameter-type.
Add swap-params to higher.rkt.
Update code to use points instead of positions.
Update positions.rkt en route to removing it.
Add random-points, which is in the documentation but did not get moved from gimplib.scm.
Correct syntax error recently introduced into drawings.rkt.
Refine the 'image-draw-arrow\!' procedure.
Add support for arrow type in turtle-show.
Add features to turtles.rkt.
* Now have turtle-show! and turtle-hide! that show/hide the turtle.
* Now have turtle-col, turtle-row, and turtle-angle.
* Some other minor cleanup.
Add 'turtle-point'.
Update strategy for guarding turtle procedures.
Update documentation and precondition testing for 'turtle-set-brush\!'
Add the swapped versions of the drawing procedures.
Fix bug in scale-drawing.
Remove rgb.rkt, which doesn't seem to be used.
Rearrange the color library

* Move functions from colors.rkt to irgb.rkt, hsv.rkt (new)
  color-name.rkt and rgb-list.rkt.
* Add some utility procedure (particularly guards for the four types).
* Promote irgb functions and deprecate rgb functions.
* Lots of cleanup of documentation.