* @param string $last_update Date of the last update
* @param integer $max_items Number of maximum items to fetch
* @param string $filter Feed items filter (activity, posts or comments)
* @param boolean $nocache Wether to bypass caching
*
* @return string Atom feed
* @param string $last_update Date of the last update
* @param integer $max_items Number of maximum items to fetch
* @param string $filter Feed items filter (activity, posts or comments)
* @param boolean $nocache Wether to bypass caching
*
* @return string Atom feed