5 changes (see below), to prepare this module for KJabberd

 - simple_to_xml now returns empty elements correctly (<el/>)
 - $obj->tag now optionally doesn't strip the namespace
 - paths may contain attrs, like in CSS3 selectors
 - added $el->cmp_element('tag[attr=val]') method (returns 1 or 0)
 - allow setting of attributes