update to Isabelle 608afd26a476
drop obsolete theory
update readme to Isabelle2013-2
update Isabelle version information
update URLs
Merge pull request #10 from lochbihl/master

Update to Isabelle2013-2

Thank you very much for the work. I'll prepare and do the release to Hackage (see http://hackage.haskell.org/upload). You can then just replicate my steps for the next release :-)