Checklist for official releases

 ===============================

 - test polyml-5.3.0, polyml-5.2.1, polyml-5.2, polyml-5.1, polyml-5.0, smlnj;

 - test Proof General;

 - test Scala wrapper;

 - check HTML header of library;

 - check CTRL-C, SIGINT in tty (also for external processes);

 - check persistent sessions with PG and Poly/ML 5.x;

 - Admin/update-keywords;

 - check ANNOUNCE, README, INSTALL, NEWS, COPYRIGHT, CONTRIBUTORS;

 - diff NEWS wrt. last official release, which is read-only;

 - update https://isabelle.in.tum.de/repos/website;

 - maintain Docs:

     doc-src/Dirs

     doc/Contents

 - maintain Logics:

     build

     lib/html/library_index_content.template