Function timestamp

gaussian_splatting/SIBR_viewers/src/core/system/String.cpp:154–165

	}

	std::string timestamp(const std::string & format) {
		auto now = std::time(nullptr);
#ifdef SIBR_OS_WINDOWS
		tm ltm = { 0,0,0,0,0,0,0,0,0 };
		localtime_s(&ltm, &now);
#else
		tm ltm = *(std::localtime(&now));
#endif
		std::stringstream buffer;
		buffer << std::put_time(&ltm, format.c_str());
		return buffer.str();
	}

} // namespace sirb