subdemo.icn: Program to show the turtle graphics subset

   subdemo displays various random designs in a window using the
turtle graphics subset library procedures.  Click in the window,
or enter a character on the keyboard, to start a new design.

   The following keyboard characters have meaning:

     w or W:                 random walk
     b or B:                 fractal bush (looks like "desert broom")
     s or S:                 spiral design
     p or P:                 polygon design
     t or T:                 rectangular tiling
     r or R:                 radial tiling

     \n, \r, \t, or SP:      choose design randomly
     q or Q:                 exit program

     0:                      pause drawing
     1, ... 9:               set speed of drawing (9 is fastest)