Parser: Take 'content' by const reference.

iparser.h

@@ -8,10 +8,10 @@
 class IParser
 {
   public:
-	virtual std::string extractCommand(std::string cmdname, std::string content) const = 0;
-	virtual std::vector<Headline> extractHeadlines(std::string content) const = 0;
-	virtual std::string parse(const PageDao &pagedao, UrlProvider &provider, std::string content) const = 0;
-	virtual std::vector<std::string> extractCategories(std::string content) const = 0;
+	virtual std::string extractCommand(std::string cmdname, const std::string &content) const = 0;
+	virtual std::vector<Headline> extractHeadlines(const std::string &content) const = 0;
+	virtual std::string parse(const PageDao &pagedao, UrlProvider &provider, const std::string &content) const = 0;
+	virtual std::vector<std::string> extractCategories(const std::string &content) const = 0;
 
 	virtual ~IParser(){};
 };