Creates a new user font-face.
Use the setter functions to associate callbacks with the returned
user font. The only mandatory callback is render_glyph.
After the font-face is created, the user can attach arbitrary data
(the actual font data) to it using cairo_font_face_set_user_data()
and access it from the user-font callbacks by using
cairo_scaled_font_get_font_face() followed by
cairo_font_face_get_user_data().
Since 1.8
Creates a new user font-face. Use the setter functions to associate callbacks with the returned user font. The only mandatory callback is render_glyph. After the font-face is created, the user can attach arbitrary data (the actual font data) to it using cairo_font_face_set_user_data() and access it from the user-font callbacks by using cairo_scaled_font_get_font_face() followed by cairo_font_face_get_user_data(). Since 1.8