The changes include:

The changes include:

- moved function atk_text_set_run_attributes() to
atk_editable_text_set_run_attributes()

- defined an enum AtkXYCoords in Atktext.h

- moved definitions of AtkAttribute and AtkAttributeSet from atktext.h to
atkobject.h (temporary solution until we decide a better place to define them).

- Added extra param to atk_text_get_character_extents() and
atk_text_get_offset_at_point() of type AtkXYCoords.

I decided to make AtkAttributeSet a singly-linked list (a GSList) instead of a
doubley-linked list (a GList). There is no need for it to be doubley-linked
which is less efficient.