docs: function formatHelpMsg(usage, options) {
    var prog = path.basename(
        process.argv[0]) + ' ' + path.basename(process.argv[1]);
    var help = [
      usage.replace(/\$0\b/g, prog),
      '',
      'Options:',
      formatOption('help', 'Show this message and exit')
    ];
  
    Object.keys(options).sort().forEach(function(key) {
      help.push(formatOption(key, options[key].help));
    });
  
    help.push('');
  
    return help.join('\n');
  }