new datatype theory, supports 'draft theories' and incremental extension: add_classes, add_defsort, add_types, add_tyabbrs, add_tyabbrs_i, add_arities, add_consts, add_consts_i, add_syntax, add_syntax_i, add_trfuns, add_trrules, add_axioms, add_axioms_i, add_thyname; added merge_thy_list for multiple merges and extend-merges; added rep_theory, subthy, eq_thy, cert_axm, read_axm; changed type of axioms_of; renamed internal merge_theories to merge_thm_sgs; various internal changes of thm and theory related code;