private static void usage() {
        info("Usage: java org.yinwang.rubysonar.dump <project-dir> <out-root> <include-paths> <source-paths>... ");
        info("  <project-dir> is path to the project's root, used to determine whether symbols should be exported");
        info("  <out-root> is the prefix of the output files.  There are 2 output files: <out-root>-sym, <out-root>-ref");
        info("  <include-paths> are colon-separated paths to included libs");
        info("  <source-paths>... are space-separated paths to source units (.rb files) that will be graphed");
    }