* isatool mkdir provides easy setup of Isabelle session directories,
including proper documents;
* generated LaTeX sources are now deleted after successful run
(isatool document -c); may retain a copy somewhere else via -D option
of isatool usedir;
* old-style theories now produce (crude) LaTeX sources as well;
* compression of ML heaps images may now be controlled via -c option
of isabelle and isatool usedir;