message: Add a capability for the registered keywords to be cleared.
diff: @@ -54,6 +54,8 @@ namespace commonItems
  void parseStream(std::istream& theStream);
  void parseFile(const std::string& filename);
  + void clearRegisteredKeywords() { registeredKeywords.clear(); }
  +
  std::optional<std::string> getNextToken(std::istream& theStream);
  std::optional<std::string> getNextTokenWithoutMatching(std::istream& theStream);
  