Standard apertures are circle, rect, oblong and polygon (regular polygonal shapes with 3 to 12 vertices)
The support of the standard aperture type polygon was missing in Gerber plotter.
This corrects an issue with fill segments-per-circle and moves the error
to segmetns calculation down in a number of functions to expose the
single value for approximation
Allows 0 to 4 chamfered corners, not only one.
A custom shape allow this kind of shape. However because it is a primitive,
it is easier to edit and it support thermal reliefs.