Modernize our package metadata in the following ways:
* switch from description-file to long_description with the file
attribute, and specify an explicit content type and encoding
* replace the home-page parameter with the newer general url one
* use the specific license metadata in addition to the corresponding
trove classifier for it
* make sure wheels when built also incorporate the LICENSE and
AUTHORS files so that we're not distributing them without a copy
of the license text
* indicate support for all recent Python releases in trove
classifiers
* drop Python 3.4 cruft from the bindep list
https://setuptools.readthedocs.io/en/latest/userguide/declarative_config.html
Also replace the contributor documentation with a more up to date
copy from opendev/bindep, and adjust the copyright assertions in the
built Sphinx docs to refer to "OpenDev Contributors" and drop the
unnecessary year.
Change-Id: I39c5f5afc66edec0cf51709218f143b2a749eddd
aa21a0c61b