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