add new sort functions
add action to the dlna_item_metadata function

the action allows to use the profiler to retrieve the metadata or remove or change, and to use the less memory as possible (when the provider can do it)
Example:
 request the metadata of the item
 and release them when it's not more usefull.
 metadata = dlna_item_metadata (item, GET);
 printf (metadata->title);
 dlna_item_metadata (item, FREE);