A Curve structure containing all the points with integer coordinates in
the disc $x^2+y^2 \leq r^2$ is created by this module.
It is recommended to choose $r$ half-integer 
(e.g. $r=1.5, 2.5, \ldots$) to produce more ``circular'' discretized shapes.
With the \verb+-i+ option, the points such that
$x^2+y^2 \leq i^2$ are deleted from the output curve.