Support Unicode and long-paths on Windows

[mnightingale]

Adds support for Unicode program arguments and long-paths using the \\?\ prefix on Windows.
Also converts filenames to the codepage in use by the console, so if supported won't result in question marks in the output.

The changes should have no affect on non-Windows builds, the utf8::* methods are no-ops.

References to a few useful resources used to arrive at this solution:

• https://github.com/alf-p-steinbach/C---how-to---make-non-English-text-work-in-Windows/blob/main/how-to-use-utf8-in-windows.md the app-manifest.xml approach could have been useful but it appears to be require Windows 10, hence the wmain wrapper.
• https://utf8everywhere.org

Resolves #189

[Safihre]

@animetosho since there's not really a maintainer, maybe you could code review and pull the changes into par2cmdline turbo?
And maybe the same for #182 ?

[animetosho]

Unfortunately I already stretched myself too thin with par2cmdline-turbo, so I want to stay far away from par2cmdline maintainer duties.

Appreciate the work people have put in with pull requests regardless - it goes to show there's still interest in the project. Perhaps this interest could lead to a new maintainer - maybe see if someone else is willing?