cmdline parser

    // If no image path was given, then supply some information on how this tool works
    const char *keys =
            "{ help h ?       |               | show this message }"
            "{ images i       |               | folder_location }"
            "{ annotations a  |annotations.txt| ouput_file }"
            ;

    CommandLineParser parser(argc, argv, keys);
    String image_folder = parser.get<String>("images");
    String annotations = parser.get<String>("annotations");
    if (parser.has("help") || image_folder.empty())
    {
        parser.printMessage();
        cerr << "Example:  annotate -i=/data/testimages/ -a=/data/annotations.txt" << endl << endl;
        return -1;
    }