See Section 26.9.2 for regular polygons in the plane.
The isopolygon
command creates regular polygons in space.
isopolygon takes four arguments:
A,B,P, three points.
k, an integer.
isopolygon(A,B,P,k) returns and draws a regular
polygon with one edge AB in the plane ABP with |k| sides.
If |k| is positive, then the polygon is positively oriented,
otherwise it is negatively oriented.
