default and custom error pages response

+ refactoring in response.cpp (functions split)
+ added Client::clear()
+ added replace_all_substr() in utils.cpp

srcs/utils.cpp

@@ -84,3 +84,18 @@ std::string	http_methods_to_str(unsigned int methods)
 
 	return (str);
 }
+
+void	replace_all_substr(std::string &str, const std::string &ori_substr, const std::string &new_substr)
+{
+	if (ori_substr.empty())
+		return;
+	size_t	pos = 0;
+	while (1)
+	{
+		pos = str.find(ori_substr, pos);
+		if (pos == std::string::npos)
+			break;
+		str.replace(pos, ori_substr.size(), new_substr);
+		pos += new_substr.size();
+	}
+}