Draw an n-sided polygon, ending up with the turtle
being where it started out and facing the same
direction, and with the pen properties the same, too.
Draw a spiral of n lines, beginning at the current turtle
position and angle, using an angle of ang between adjacent
lines and pausing ms milliseconds after each line.
Make the graphics panel as big as possible, clear the panel, and
draw a Sierpinksi triangle of depth d with side length s
with the bottom left corner (x,y).