message: use const references where it makes sense
diff: @@ -570,7 +570,7 @@ class Builder {
  private:
  inline void checkKeyIsString(bool isString) {
  if (!_stack.empty()) {
  - ValueLength const tos = _stack.back();
  + ValueLength const& tos = _stack.back();
  if (_start[tos] == 0x0b || _start[tos] == 0x14) {
  if (!_keyWritten && !isString) {
  throw Exception(Exception::BuilderKeyMustBeString);
  @@ -612,7 +612,7 @@ class Builder {
  uint8_t* addInternal(std::string const& attrName, T const& sub) {
  bool haveReported = false;
  if (!_stack.empty()) {
  - ValueLength& tos = _stack.back();
  + ValueLength const& tos = _stack.back();
  if (_start[tos] != 0x0b && _start[tos] != 0x14) {
  throw Exception(Exception::BuilderNeedOpenObject);
  }
  