handle utf8 file names

[jschueller]

hello,
another problem I had is that rapidcsv cannot open file which names contains utf8 chars
I had to patch to something like thing to enable the wide char apis on windows:

    void ReadCsv()
    {
      std::ifstream stream;
      stream.exceptions(std::ifstream::failbit | std::ifstream::badbit);
#ifdef RAPIDCSV_ENABLE_CXX17
      stream.open(std::filesystem::u8path(mPath), std::ios::binary);
#else
      stream.open(mPath, std::ios::binary);
#endif
      ReadCsv(stream);
    }