minetest.get pointed thing position

Description
Get position of a pointed_thing (that you can get from somewhere).
 * If pointing at a node & above -> return pointed_thing.above
 * If pointing at a node & not above -> return pointed_thing.under
 * If pointing at a objec & object exists -> return object position
 * If pointing at a objec & object does not exists -> return nil
 * If none of the above -> return nil