Issue #22394: Add a 'venv' command to Doc/Makefile.

This will create a venv using the interpreter specified by the PYTHON
variable for the Makefile that also install Sphinx. Typical usage is
expected to be:

  cd Doc
  make venv PYTHON=../python
  make html PYTHON=venv/bin/python3
Issue #22581: Use more "bytes-like object" throughout the docs and comments.
Issue #22581: Use more "bytes-like object" throughout the docs and comments.
Merge heads