fix docs and add clone and reversed iterator calls.

fix docs and add clone and reversed iterator calls.

 * docs: be clear if it's a copy or in-place.

 * clone: add some apis to create a copy while operates, sort should
   do the same.

 * reversed iterator: new call to walk the list reversed, will make
   life easier in some cases.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/eina@39515 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33