setuptools and Windows

[jpgrayson]

In PR #103, which has been outstanding for some time now, there are a bunch of distinct changes/capabilities all aimed at improving StGit's support for Windows. As of this writing, a couple pieces of this PR have been implemented separately and merged. Here's the summary:

• PEP-440 changes (311caea)
• Find viable bash.exe for running hooks (ed16517)
• Use setuptools for packaging StGit (work-in-progress)
• Make stg executable available as a console_script entrypoint (work-in-progress)
• Allow test suite to run on Windows

I've historically been reluctant to use setuptools for StGit's packaging. The rationale was threefold:

1. It was possible to sufficiently package StGit with distutils from the Python standard library.
2. setuptools would become StGit's first required build-time dependency
3. Modern setuptools based packaging would enable StGit to be distributed via pip and PyPI, which I consider an anti-feature since StGit is an end-user application which only is only incidentally implemented in Python.

Whelp, PEP-632 officially deprecates distutils and points to setuptools as the blessed replacement. And distutils will eventually be removed from the Python standard library.

So, that seems like a pretty good reason for StGit to use setuptools. And I am working on this.

The next capability from #103 is deploying stg as a console_script entrypoint instead of a script. This is the standard approach for modern python applications. I've used it extensively in other projects. The difficulty for StGit is retaining an acceptable development workflow. I.e. we need to be able to run the test suite and/or individual tests without imposing new prerequisite steps after each code change. Using "deveop mode" (i.e. pip install -e or setup.py develop) will probably become necessary. I need to work out the edge cases and account for StGit's auto-generated builtin_version.py and cmdlist.py files.

Help Wanted

The last piece will be making sure all of the above works on Windows, including the test suite. It would also be great to have continuous integration run on Windows. GitHub Actions supports this, so it feels like this is within reach.