gradient (Imlib2::Image)

    /*
     * Fill a rectangle with the given Imlib2::Gradient at a given angle
     *
     * Examples:
     *   x, y, w, h = 10, 10, image.width - 20, image.height - 20
     *   angle = 45.2
     *   image.fill_gradient gradient, x, y, w, h, angle
     *
     *   rect = [5, 5, 500, 20]
     *   image.gradient gradient, rect, 36.8
     *
     */
    static VALUE image_fill_gradient(int argc, VALUE *argv, VALUE self) {