Automatic 2d Fillet in OpenSCAD

// This routine creates a fillet between two arbitrary shapes. // It works by expanding each shape by some distance and then creating a very thin shell around these expanded shapes. These two shells are then intersected to give one point along the fillet. The distances are chosen so that, for a two shapes that intersect under right angle, these intersection points lie on a quarter circle, with fn_fillet=16 faces.
// The hull() command is then used to hull two adjacent intersection points together, thus creating the fillet.
// This method has two side effects:
// The fillet is not flush with the two shapes but sticks out by a small amount of dr=0.005, the thickness of the shells used to create the intersection points.
// secondly, this routine creates a bulge around places were the two original shapes overlap. As illustrated in example 5 and example 6. This excess budge needs to be trimmed by hand.
// Sometimes it is also possible to avoid this excess bulge by smart choice o