Revision 512421

- Fix documentation build
- Add textproc/py-sphinx_rtd_theme and textproc/towncrier to build dependencies
- Add files/patch-docs_conf.py to fix ModuleNotFoundError (virtualenv)
- Set LANG and LC_ALL environment variables to mitigate a RuntimeError during the
  build stage of the doc.:

  RuntimeError: Click will abort further execution because Python 3 was configured to use ASCII as encoding for the environment. Consult https://click.palletsprojects.com/en/7.x/python3/ for mitigation steps.