Separate oauthlib integration into its own package (#137)

* Centralize the run_pylint script.
* Use io.open instead of open in setup.py for httplib2_transport
* Move httplib2_transport -> additional_packages/google_auth_httplib2
* Remove unneeded dependencies in google_auth_httplib2
* Update classifiers to note 3.6 support.
* Don't install the HEAD version of google-auth when testing google-auth-httplib2.
* Add google-auth-oauthlib package.
* Remove google.oauth2.oauthlib and google.oauth2.flow and associated tests.
* Make travis run google-auth-oauthlib's tox.
* Specify tox workdir.
33 files changed