re-implemented build_doc in Isabelle/Scala;
clarified command-line: specify documentation files (via document_variants) instead of sessions;
syntax: glob
*~
*.class
*.jar
*.orig
*.rej
.DS_Store
.swp
syntax: regexp
^contrib
^heaps/
^browser_info/
^doc/.*\.dvi
^doc/.*\.eps
^doc/.*\.pdf
^doc/.*\.ps
^src/Tools/jEdit/dist/