added cheating, sorry_text (from skip_proofs.ML); added method_setup (from isar_thy.ML);

load late, after proof.ML; added goal commands: theorem, interpretation etc.; tuned some warnings -- single line only;

moved most material to its proper place (sign.ML, pure_thy.ML, method.ML, proof.ML, locale.ML etc.); begin_theory: tuned interface, check uses in thy_info.ML;

cleanup parsers and interfaces;