code: function checkValue(config, res, key, trueVal, falseVal) {
      res[key] = (config[key] == true || config[key] == undefined || config[key] == null) ? trueVal: falseVal;
  }
docs: General Default markdown-it config.
  @param  {Object} config configuration
  @param  {Object} res    configuration
  @param  {String} key    the key of config
  @param  {String} trueVal    the val of config[key] == true
  @param  {String} falseVal    the val of config[key] == false
  @return {null}