v4.0.0

New features:

New Django samples. (#636)
Add support for RFC7636 PKCE. (#588)
Release as a universal wheel. (#665)
Bug fixes:

Fix django authorization redirect by correctly checking validity of credentials. (#651)
Correct query loss when using parse_qsl to dict. (#622)
Switch django models from pickle to jsonpickle. (#614)
Support new MIDDLEWARE Django 1.10 setting. (#623)
Remove usage of os.environ.setdefault. (#621)
Handle missing storage files correctly. (#576)
Try to revoke token with POST when getting a 405. (#662)
Internal changes:

Use transport module for GCE environment check. (#612)
Remove author lines and add contributors.md. (#627)
Clean up imports. (#625)
Use transport.request in tests. (#607)
Drop unittest2 dependency (#610)
Remove backslash line continuations. (#608)
Use transport helpers in system tests. (#606)
Clean up usage of HTTP mocks in tests. (#605)
Remove all uses of MagicMock. (#598)
Migrate test runner to pytest. (#569)
Merge util.py and _helpers.py. (#579)
Remove httplib2 imports from non-transport modules. (#577)
Breaking changes:

Drop Python 3.3 support. (#603)
Drop Python 2.6 support. (#590)
Remove multistore_file. (#589)