Problem: xrefcheck uses utf8 symbols in reports, which are not supported
on most of Windows shells by default.
Sometimes they are printed as question marks (and it cause golden tests to fail)
and sometimes printing of them raise an error.

Solution: use function `withCP65001` from `code-page` package which
sets correct codepage on Windows and do nothing on other OSs

Problem: in markdown links, '/' should always be used as path separator ,
e.g. GitHub renderer is not threating link `[x](a\b.md)` as a link
to file in dir `a`
We use OS-dependent file separators everywhere, so
e.g. `canonizeLocalRef "./a.md"="./a.md`"` on Windows

Solution: replace '\' to '/' while constructing repo tree if needed
and then use only '/', preferring functions from `System.FilePath.Posix`.
We can do this, since 'a/b' and `a\b` are equivalent paths on Windows

Problem: we are not testing behavior of xrefcheck on Windows

Solution: and add workflow to run
golden and tasty tests on CI
via github-actions windows runner
Some subproblems appear:

1.
Problem: CI build fails beacuse it needs `pcre` package
Solution: add it (somehow), see `install pacman dependencies`
in ci.yml

2.
Problem: Network errors displayed different on different platforms
Solution: collect output from both and use
`assert_diff expected_linux.gold || assert_diff expected_windows.gold`

3:
Problem: "Config matches" test is failing because checkout action
clone files with CRLF, and test assert equality of two ByteStrings
Solution: manually remove CR