Release version 2.0-000

Using tarball (with SHA1):
2aea3ec17b512b8f24eb0ba1b6bc53e6cd49e386 *Vrui-2.0-000.tar.gz
Release version 3.1-001

Using tarball (with SHA1):
8b258cc5db7d94b1352f2defa935743a9b45b9f3 *Vrui-3.1-001.tar.gz