Parser: Add callback support for unknown "tags"

parser.h

@@ -11,9 +11,12 @@ class Parser : public IParser
 	std::string extractCommand(std::string cmdname, const std::string &content) const;
 	std::vector<Headline> extractHeadlines(const std::string &content) const override;
 	std::vector<std::string> extractCategories(const std::string &content) const override;
-	std::string parse(const PageDao &pagedao, UrlProvider &provider, const std::string &content) const override;
+	using IParser::parse;
+	virtual std::string parse(
+		const PageDao &pagedao, UrlProvider &provider, const std::string &content,
+		const std::function<std::string(std::string_view, std::string_view)> &callback) const override;
+
 	using IParser::IParser;
-	~Parser(){};
 };
 
 #endif // PARSER_H