The setup.py test command and pytest-runner have been deprecated for
several years and are no longer recommended. The pytest documentation
no longer recommends pytest-runner and their own documentation
recommends against it.

- https://github.com/pypa/setuptools/issues/1684
- https://github.com/pytest-dev/pytest/issues/5534
- https://github.com/pytest-dev/pytest-runner/issues/50

Changes made:

- Removed pytest-runner: Eliminated the use of pytest-runner from
  `setup.py`.
- Moved test dependencies to the `extra-dependencies`, which can be used
  by tox as well as for manual installation.
- Updated the documentation to recommend using tox as the default test
  runner. Alternatively, users can manually run tests with the `py.test`
  command.

These changes will also make an eventual migration to `pyproject.toml`
easier, as the `extras_require` can be copied to the
`project.optional-dependencies` section.

This commit refactors the codebase to consistently use Python 3.6
f-strings for string concatenation and interpolation.

BREAKING CHANGE: This update increases the minimum required Python
version from 3.5 to 3.6. Python 3.5 reached end-of-life in September
2020 (~4 years ago) and has been dropped from most distributions, so the
impact on users should be minimal.

This commit updates some outdated syntax with the modern alternatives.
The changes were applied automatically using pyupgrade (v2.0.1) with the
following command:

```
pyupgrade --py3-plus **/*.py
```

These updates are purely syntactical and there should be no change in
functionality.

This is based on
https://packaging.python.org/en/latest/guides/publishing-package-distribution-releases-using-github-actions-ci-cd-workflows/#defining-a-workflow-job-environment
. It's the sample config from there, with versions updated and
our project name substituted in the appropriate places. I dropped
the publish-to-testpypi bit because of
https://github.com/pypa/packaging.python.org/issues/804

 , and left
the Github release part left out for now. We can add that later if
we like, but we never published releases to Github before, so it
doesn't seem required yet. I also tweaked the conditionals a bit
to avoid running the build job on forks and publish only tags
that start with 'v', as that's our convention for versions.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

Add missing classifiers for Python versions >= 3.9

* `Iterator.next()`` has been replaced with `Iterator.__next__()`
* The `object.__unicode__()` method is not used anymore
* Default source encoding has changed from ASCII to UTF-8

test_client.py uses pkg_resources. That's part of setuptools,
not Python. Per
https://docs.python.org/3.12/whatsnew/3.12.html#removed

 , it
was previously included by default in venv environments, but no
longer is from 3.12 onwards, so we need to explicitly require
setuptools to ensure it's available.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

mock was included in unittest in python 3.3

requests_oauthlib dependency name will only install from pip, requests-oauthlib works on both conda and pip

Python 3.4 is EOL and support for it has been removed by
the requests package that we depend on.

Python 3.3 is EOL, and is failing on Travis.

This optimizes setup.py for cases when pytest-runner is not needed,
using the approach that is suggested upstream:

https://pypi.python.org/pypi/pytest-runner#conditional-requirement

This reverts commit 1650e0e7.
Upstream restored handling of the adding_headers arg in 0.6.1.
Going back to using that name means we're still compatible with
any version of responses after 0.3.0, except 0.6.0. Also adjust
setup.py to express this correctly.

Remove python2.6 from
- Travis
- Tox
- PyPi tags
- documentation and readme

Also, Simplify an import clause.

This fixes #133

Looks like a buggy pip version could be the root cause, but
nevertheless, we shouldn't need to specify that we're depending on
requests explicitly when requests_oauthlib depends on it.

(https://stackoverflow.com/questions/27497470/setuptools-finds-wrong-package-during-install)

Add OAuth and update docs