UTF16 and Conhost support for Windows

[oshaboy]

this adds 2 new options
--utf16 output using WriteConsoleW
--format conhost use Legacy Windows Console API (implies --utf16)

[oshaboy]

Oh right there's also --encoding which converts utf-8 to a legacy codepage using iconv

[hpjansson]

This looks pretty good overall. My main requests are that we leave the UTF-16 switch/WriteConsoleW() code out for now and focus on the direct Conhost output, plus a raft of small stylistic changes.

Thanks a lot for doing this!