fix license

updated source files with Metis 2.3 (timestamp: 16 Sept. 2010)

MIT license -> BSD License

copied the unmodified official Metis 2.3 (15 Sept. 2010) sources into Isabelle

change license, with Joe Hurd's permission

new version of the Metis files

remove old sources

GPL -> BSD

The Metis prover (slightly modified version from Larry);