code: function signature(opt) {
  
    var options = opt || Object.create(null);
    var my = {
      header: String(options.header || 'Server'),
      signature: String(options.signature || 'Nodejs'),
      token: String(options.token || 'Full'),
      custom: options.custom,
      extra: options.extra,
      standalone: Boolean(options.standalone)
    };
    if (my.token == 'Full') {
      my.Prod = my.Major = my.Minor = my.Min = my.OS = true;
    } else if (my.token == 'OS') {
      my.Prod = my.Major = my.Minor = my.Min = my.OS = true;
    } else if (my.token == 'Min') {
      my.Prod = my.Major = my.Minor = my.Min = true;
    } else if (my.token == 'Minor') {
      my.Prod = my.Major = my.Minor = true;
    } else if (my.token == 'Major') {
      my.Prod = my.Major = true;
    } else if (my.token == 'Prod') {
      my.Prod = true;
    }
    return wrapper(my);
  }
docs: option setting
  
  @exports signature
  @function signature
  @param {Object} opt - various options. Check README.md
  @return {Object}