Set up symlinks for (a subset of) the pwny apps.

def symlink(parser, cmd, args):
    """
    Set up symlinks for (a subset of) the pwny apps.
    """

    parser.add_argument(
        'apps',
        nargs=argparse.REMAINDER,
        help='Which apps to create symlinks for.'
    )
    args = parser.parse_args(args)

    base_dir, pwny_main = os.path.split(sys.argv[0])

    for app_name, config in MAIN_FUNCTIONS.items():
        if not config['symlink'] or (args.apps and app_name not in args.apps):
            continue
        dest = os.path.join(base_dir, app_name)
        if not os.path.exists(dest):
            print('Creating symlink %s' % dest)
            os.symlink(pwny_main, dest)
        else:
            print('Not creating symlink %s (file already exists)' % dest)