evas_map: more extensible and safe. add docs

evas_map: more extensible and safe. add docs

change evas_map to return a structure that serves as an array of
points. This way we'll know for sure the number of points in it. Right
now it's hardcoded to 4, so check it, but in future we can just allow
more points and it should work.

added docs. I'm not sure about most of it, so it would be good to have
someone to review and fill in more, maybe that's raster? Grep for
"TODO" and you'll see the missing stuff. It would be good to add
examples in evas_map_point_coord_set() and
evas_map_point_image_uv_set()

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/evas@43211 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33