parser: Add [content] tag, add extractFirstTag() method

iparser.h

@@ -15,6 +15,7 @@ class IParser
 	}
 
   public:
+	virtual std::string extractFirstTag(std::string tagname, const std::string &content) const = 0;
 	virtual std::string extractCommand(std::string cmdname, const std::string &content) const = 0;
 	virtual std::vector<std::string> extractCommands(std::string cmdname, const std::string &content) const = 0;