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

* add specific labelled project links for improved navigation from
  PyPI's summary sidebar

* add commandline keyword to help folks searching

* 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

* stop flagging wheels as "universal" now that git-review no longer
  supports Python 2.7

* drop the old Sphinx integration config for PBR now that it's no
  longer needed

https://setuptools.readthedocs.io/en/latest/userguide/declarative_config.html

Also update old openstack.org URLs throughout contributor docs and
examples/comments to newer opendev.org counterparts. Remove the old
redundant HACKING.rst file as well as a lingering MANIFEST.in from
the times before PBR was a thing. Replace the CONTRIBUTING.rst with
a shorter one cribbed from bindep. Add the test profile to the one
entry in bindep.txt to make it more apparent that's not a runtime
dependency of git-review. Adjust some old "OpenStack, LLC."
copyrights as indicated by the foundation's "Legal Issues FAQ."

Change-Id: Ie45d4d73ba7b5a860f09cc4f1d849587761d846c