Fixes https://github.com/fonttools/fonttools/issues/1141 Uses code from Chromium Blink's SVG path parser, in SVGPathNormalizer::DecomposeArcToCubic https://github.com/chromium/chromium/blob/master/third_party/blink/renderer/core/svg/svg_path_parser.cc#L169-L278 Each elliptical arc is approximated by series of cubic bezier curves, one cubic every 90-degree portion of an arc.