BSpline Curves

igds_type: igds_line

This is stored as an IGDS type 27 element. The information of the poles, knots and weights of a spline are stored in element types 21, 26 and 28 respectively. Currently, only reading of bsplines is supported. The bsplines are read and stroked into segments (which is why its igds_type is stored as igds_line).