Made `Gfx2d::draw` return generic type
Made `Gfx2d::draw` return generic type

Closes https://github.com/PistonDevelopers/gfx_graphics/issues/296

bvssvni/gfx_graphics,kvark/gfx_graphics,PistonDevelopers/gfx_graphics,mitchmindtree/gfx_graphics