This adds read/write support for arcs in polygons (DRAWSEGMENT, EDGE_MODULE and zone outlines)
Read/write file formats
Plot arcs as part of polygons
Convert clipper results to lines/arcs
Clipper does not make it feasible to pass a polygon through and get the related points back, even if you are only doing a boolean operation. All points get scrambled/re-written. So maintaining zones with arcs will require recognizing/converting arcs post-clipper.
Drawing polygons with arcs is part of !374