Emscripten support

[curiousdannii]

Emscripten doesn't bundle the zoneinfo file, but it does support the libc and C++ time libraries, through which you can get the timezone.

Would it be in scope to use the libc functions in this crate, or is this really purely about searching zoneinfo, so that Emscripten support would need to be pushed up to Chrono etc?

Looks like Windows is using a completely different method, so I guess it would be fine for Emscripten support to go through libc then?

Oh, but I see this crate is about returning a timezone name, not just an offset. I don't think you can do that in libc, and I'm not sure if that part of the C++ lib is supported in Emscripten. It might be better to just ask Chrono to use libc for its calculations.