added command 'SML_export' and 'SML_import' for exchange of toplevel bindings;
obsolete since polyml-5.5.0;
obsolete for release;
removed odd context argument: Thy_Info.get_theory does not fit into PIDE document model;
clarified tooltip_lines: HTML.encode already takes care of newline (but not space);
more elementary option sledgehammer_provers, avoiding complications of defaults from ML side (NB: guessing at number of cores does not make sense in PIDE);
clarified actor plumbing;
sos accepts False, returns apply command
swap with qualifier;
tuned