cleanup in item::* namespace most functions were already moved into the content::item namespace, but a few were left.
- marked the following function as deprecated * item::get_content * item::content_is_null * item::get_revision_content * item::content_methods_by_type * item::publish * item::unpublish
- mark more of the functions in the ::item::* namespace as deprecated, since much of the detailed info is delivered by ::content::item::get * item::get_mime_info * item::get_extended_url * item::get_element