problem reading utf8 filenames on windows

[andreprager]

I'm facing an issue reading waves from filenames containing chinese or other language specific characters. I'm using Visual Studio 2019 on Windows 10.
I made a local branch where I added std::wstring support, which at least solved the issue on my side.
I will now try to make a pull request (never did it before) so that you can review and hopefully merge it to main branch, so that others don't need to invest as much time as I did to find the cause of the issue.

Thanks a lot for the library so far, saved me some time, well done.