Function get_standard_stream

src/indicators.hpp:834–843

Since C++ hasn't a true way to extract stream handler from the a given `std::ostream` object, I have to write this kind of hack.

        //! from the a given `std::ostream` object, I have to write
        //! this kind of hack.
        inline
        FILE* get_standard_stream(const std::ostream& stream)
        {
            if (&stream == &std::cout)
                return stdout;
            else if ((&stream == &std::cerr) || (&stream == &std::clog))
                return stderr;

            return nullptr;
        }

        // Say whether a given stream should be colorized or not. It's always
        // true for ATTY streams and may be true for streams marked with