(Windows) Set console to UTF-8 on init

[anzz1]

From my testing this fixes the problems with UTF-8 inputs and outputs.

I dislike having to add this platform-specific code but it has to be done for it to work properly. The only other option would be guiding users to go deep into settings to enable a "beta" UTF-8 feature...sigh.

At least is wrapped somewhat nicely as its' own function outside the main loop.

[lofcz]

tested on win, LGTM. Considering the previous UTF-8 hack this replaces, I'd say it's better done this way.

[ggerganov]

Can merge after conflicts are resolved

[Estelle-gqy]

your comit contains main.cpp file, but the master branch I cloned does not contain this file, how can I fix the bug？