code: function Request_hasHeader(key) {
          if (Type.isString(key)) {
              return this.headers.hasOwnProperty(key.toLowerCase());
          } else {
              throw new error.HttpError(500, {key: key}, "Request.hasHeader: Header key must be string type");
          }
      }
docs: @since 0.0.1
  @author Igor Ivanovic
  @method Request#hasHeader
  
  @description
  Has header