Make autogen work under Windows+MSVC

[KubaO]

1. Default encoding on Windows isn't UTF-8. This caused autogen to mangle the documentation files.
2. Add detection of MSVC so that autogen will work under msvc command line.

This helps when using hpy under MSVC.

[fangerer]

Thanks for your contribution. In general, looks good to me. Maybe just remove the unused variable and then I'm happy to merge (if tests are passing, ofc).

[KubaO]

We don't care about Python 2.7 anymore, right?

[fangerer]

We don't care about Python 2.7 anymore, right?

Hi @KubaO, please excuse my very late answer. We don't really care about Python 2.7 in the sense that we don't run or support HPy on Python 2.7. However, we are running tests on PyPy and some of the test files therefore also need to be Python 2.7 compatible. Anyway, @mattip already has a fix (see #444 ).

[mattip]

Just to be clear: #444 fixes the CI startup failure for 2.7, but if you want to use open with encoding, that won't work on 2.7. So if these code paths are hit when running

python2.7 test/check_py27_compat.py

then the 2.7 CI job will still fail, since that is the command it runs.

Running this PR locally, everything here seems fine.

[mattip]

Close/reopen to trigger CI