Make it possible to create iterators outside Eina.

Make it possible to create iterators outside Eina.

Many places in EFL we just create walk something, create a list with
walked data, return, then the user walks it again and then deletes
(which will walk again). For such cases it's way better to define
iterators or accessors.

I'm not moving any EFL code to it now, but if people are interested,
things like evas_render_method_list(), evas_font_available_list(),
evas_objects_at_xy_get(), evas_objects_in_rectangle_get(),
evas_object_smart_members_get() are good candidates. If the subject is
already using Eina list, then you can just use
eina_list_iterator_new() and return it, otherwise you can define your
own iterator, which is very easy.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/eina@37956 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33