v0.11.0: Merge pull request #94 from hfutrell/intersection-via-implicitization

-- uses much faster analytical method for curve.selfIntersections. Removed accuracy parameter since it is no longer needed there (self intersections will always be found with very high accuracy).
-- improves curve-curve intersection performance (curve.intersections(with:)) in certain cases such as when requesting very precise accuracy or when curves intersect tangentially.