Add command line option for exporting version information.

def add_subparser(subparsers):
    """Add command line option for exporting version information.
    """
    parser = subparsers.add_parser("version",
                                   help="Export versions of used software to stdout or a file ")
    parser.add_argument("--workdir", help="Directory export programs to in workdir/provenance/programs.txt",
                        default=None)