changed Markup print mode to YXML -- explicitly decode messages before being issued;
changed Output print mode to plain default -- no escaping;
simplified pgml_sym: produce Pgml.pgmlatom, no special treatment of Ctrl/Raw;
removed unused issue_pgips;
removed obsolete delay_msgs feature -- the script parser never fails, but produces inline error markup;
removed obsolete wrap_pgml;
explicit transformation of messages (pgml_terms and message_content);
remove obsolete split_markup workaround;
misc tuning;
