[cairo] [RFC] Color space API (partial proposal)

[ecir hana]

E.g.:

/* Create a Device N color space. alternate_color_space specifies
  * the color space to be used for the alternative colors for each
  * component
  */
  cairo_color_space_t *
  cairo_color_space_create_device_n (
                      cairo_color_space_t *alternate_cmyk_space)

/* Add a colorant to the DeviceN color space. "name" is the name of the
  * colorant. alternate_color is an array of components specifying the
  * a color in the alternate_color_space.
  */
  void
  cairo_color_space_add_colorant (
                                  const char          *name,
                                  double              *tints)