Add simple support for xml output if the third party dict2xml.py module https://pypi.org/project/dict2xml/ is installed. Also this checkin adds the ETag support comment to the CHANGES document. The file was accidently omitted from the rest of the etag checkin.

@rem python -m pip install sphinx
@rem python -m pip install sphinxcontrib-cheeseshop

python -m sphinx . html