Gradient fills in libHaru

Gradient fills in the PDF specification are handled by the 'sh' operator. The current libHaru code (2.2.1) does not implement the PDF shading specification (using the 'sh' operation) and we need an extension to libHaru that will provide this. Our minimum needs are for: (a) linear blends; and (b) mid-linear blends. The extension must support both RGB and CMYKcolorspaces, and minimally to support 0, 90, 180. and 270 degree gradient directions.