Function vstrprintf

RedEdrShared/loguru.cpp:1676–1681

#if LOGURU_USE_FMTLIB
	template<typename... Args>
	std::string vstrprintf(const char* format, const Args&... args)
	{
		auto text = textprintf(format, args...);
		std::string result = text.c_str();
		return result;
	}

	template<typename... Args>
	std::string strprintf(const char* format, const Args&... args)