New macros, documentation and consistency for iterators and accessors.

New macros, documentation and consistency for iterators and accessors.

EINA_ITERATOR_FOREACH() and EINA_ACCESSOR_FOREACH() are new macros to
help us forget about nasty C details (like cast to (void **)).

Document most iterators and accessors.

All iterators now set EINA_ERROR_OUT_OF_MEMORY if it's the case.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/eina@39267 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33