support for MSWin32

I would like to be able to use this module on Strawberry Perl, but it doesn't have I18N::Langinfo.

This makes it optional.  I don't think it is necessary to make I18N::Langinfo a prereq, since it has been in the core and should be available if the OS supports it since Perl 5.8.

I did some research on the web, and the consensus seems to be that Unicode support in a CMD.EXE / or PowerShell environment is possible, but is unreliable.  The default I believe is ASCII and thus there isn't any reason to default to UTF-8 on MSWin32.