Run Minigo in GTP mode.

def main(argv):
    """Run Minigo in GTP mode."""
    del argv
    engine = make_gtp_instance(FLAGS.load_file,
                               cgos_mode=FLAGS.cgos_mode,
                               kgs_mode=FLAGS.kgs_mode,
                               minigui_mode=FLAGS.minigui_mode)
    dbg("GTP engine ready\n")
    for msg in sys.stdin:
        if not engine.handle_msg(msg.strip()):
            break