private static void usage() {
        _.msg("Usage:  java -jar rubysonar-2.0-SNAPSHOT.jar <file-or-dir> <output-dir>");
        _.msg("Example that generates an index for Python 2.7 standard library:");
        _.msg(" java -jar rubysonar-2.0-SNAPSHOT.jar /usr/lib/python2.7 ./html");
        System.exit(0);
    }