code: func TransactionSetCategory(id int64, category string) (int, error) {
  	ccategory := C.CString(category)
  	defer C.free(unsafe.Pointer(ccategory))
  	return errNo(C.newrelic_transaction_set_category(C.long(id), ccategory))
  }
docs: /*
   * Set transaction category name, e.g. Uri in WebTransaction/Uri/<txn_name>
   *
   * @param transaction_id  id of transaction
   * @param category  name of the transaction category
   * @return  0 on success, else negative warning code or error code
   */