Sweep

Pretty much working now, sweeping along a bspline path. Learnt a bit about projecting points onto planes. In the first try, the profile was translated and orientated to the coordinate system at the division points, in this version, the polygon is projected from each plane to the next - that'll help when the path consists straight lines at sharp angles - have to now write a bit to check whether the path has any segments in it that are sharp say close to 90 degrees and then to add a plane between them at 45.