Fix issue doxygen generation issues

[FrankYFTang]

We currently still have the following warning:

inflection/dialog/SemanticFeature.hpp:67: warning: Member operator<(const SemanticFeature &other) const (function) of class inflection::dialog::SemanticFeature is not documented.
inflection/lang/features/LanguageGrammarFeatures_GrammarCategory.hpp:63: warning: Member operator<(const LanguageGrammarFeatures_GrammarCategory &other) const (function) of class inflection::lang::features::LanguageGrammarFeatures_GrammarCategory is not documented.
inflection/lang/features/LanguageGrammarFeatures_GrammarFeatures.hpp:41: warning: Member operator<(const LanguageGrammarFeatures_GrammarFeatures &other) const (function) of class inflection::lang::features::LanguageGrammarFeatures_GrammarFeatures is not documented.