automation: drop support for Python 2.7 in Windows environment
We stop installing Python 2.7 in the Windows environment.
We remove support for building Python 2.7 wheels and installers.
There is still some Python 2.7 support cleanup to perform in automation.
But this removes the biggest remaining chunk of references to 2.7.
Differential Revision: https://phab.mercurial-scm.org/D12263
Mercurial's documentation is kept in reStructuredText format, which is
a simple plain text format that's easy to read and edit:
http://docutils.sourceforge.net/rst.html
It's also convertible to a variety of other formats including standard
UNIX man page format and HTML. You'll need to install Docutils:
http://docutils.sourceforge.net/
Use the Makefile in this directory to generate the man and HTML pages.