ANN: Alpha version of Webware for Python 3

Hi all,

sorry for the long radio silence.

As the end of life for Python 2.7 is coming, I have finally taken some 
time to create a first public alpha release of the long promised new 
version of Webware for Python that targets Python 3.

The home page for Webware for Python 3 is here:
https://github.com/Cito/w4py3

Documentation is available here:
https://webware-for-python-3.readthedocs.io/

The documentation also lists the changes and explains how to migrate 
existing Webware apps for legacy Python.

Main improvements and changes:
- Use Python 3.6 or newer instead of Python 2
- Use standard packaging and installation
- Use entry points for Webware plug-ins
- Use WSGI instead of app server and adapters
- Use Sphinx/ReadTheDocs for documentation
- Use GitHub Actions to run improved test suite

The WebKit plug-in has been promoted to the top level and does not exist 
any more as a separate plug-in. PSP is still supported.

MiddleKit has been removed as a built-in plug-in and must be installed 
as a yet-to-be-created external plug-in now. If anybody has interest in 
creating such a Webware for Python 3 compatible MiddleKit and wants to 
become a maintainer, please let me know. I will gladly help, but cannot 
act as a maintainer myself any longer.

Please let me know how you like the new version, if there are any pain 
points, bugs or other problems. You can use GitHub issues, pull requests 
or the [email protected] mailing list for feedback and 
sending bug reports or improvements.

I will publish more alpha and beta releases in the next weeks depending 
on how much feedback and bug reports I will get, and hopefully we can 
then have the final 3.0 release by 2020.

-- Christoph