This is a helper function that creates a sequence of points on a circle of
r as a resolution determined by
n. It is not intended
for direct calling, and is used by the ellipse plotting function
addEllipse. NB not an exported function.
genCircle(n = 100, r)
the number of points to create around the circle. Defaults to 100.
the radius of the circle to create.
A 2 x n matrix of x and y coordinates of points on a circle.