Changes

Summary

1. more interrupts;
2. merged
3. clarified build_doc, based on Present.build_documents;
4. obsolete, build happens in clean tmp_dir;
5. redundant, see prepare_dir;
6. tuned signature;
7. build documents in Isabelle/Scala, based on generated tex files as session exports; reworked "isabelle document" for quasi-offline document builds: similar functionality included in "isabelle build -o document=pdf";
8. more operations;
9. more operations (as in Isabelle/ML);
10. tuned signature;
11. tuned;
12. mult_le_cancel_iff1, mult_le_cancel_iff2, mult_less_iff1 generalised from the real_ versions
13. merged
14. cleanup