In order to do efficient screen review, in which an assistive technology
attempts to extract text coordinate informatin from the screen and convert
it into a 2-D character format, certain new APIs are needed.

The existing APIs allow screen review, but require substantial (and often
inefficient) client processing.

New API needed:

atk_text_get_range_extents (AtkText *text, 
                            gint start_offset, gint end_offset,
                            gint *x, gint *y, 
                            gint *width, gint *height,
                            AtkCoordType *coord_type);

atk_text_get_bounded_range (AtkText *text,