contrib: split Windows requirements into multiple files Package support for Python 2 has diverged significantly. It is no longer trivial to maintain a single requirements file that supports both Python 2 and 3 because the set of packages and versions varies wildly. This commit split up the Windows requirements files so we have variants for Python 2 and 3. As part of this, I also renamed the files to have what I believe to be more reasonable naming ("win32" felt like a weird identifier to me). We can see that some package versions decreated on 2.7. This is because the old pinned versions weren't compatible with Python 2.

docutils
# Pinned to an old version because 0.20 drops Python 3 compatibility.
dulwich < 0.20 ; python_version <= '2.7'
dulwich ; python_version >= '3'
keyring
pygments
# Need to list explicitly so dependency gets pulled in when
# not running on Windows.
pywin32-ctypes