Google-auth

- Warn when using user credentials from the Cloud SDK ([266](https://github.com/googleapis/google-auth-library-python/pull/266))
- Add compute engine-based IDTokenCredentials ([236](https://github.com/googleapis/google-auth-library-python/pull/236))
- Corrected some typos ([265](https://github.com/googleapis/google-auth-library-python/pull/265))

- Raise a helpful exception when trying to refresh credentials without a refresh token. ([262](https://github.com/googleapis/google-auth-library-python/pull/262))
- Fix links to README and CONTRIBUTING in docs/index.rst. ([260](https://github.com/googleapis/google-auth-library-python/pull/260))
- Fix a typo in credentials.py. ([256](https://github.com/googleapis/google-auth-library-python/pull/256))
- Use pytest instead of py.test per upstream recommendation, dropthedot. ([255](https://github.com/googleapis/google-auth-library-python/pull/255))
- Fix typo on exemple of jwt usage ([245](https://github.com/googleapis/google-auth-library-python/pull/245))

- Added a check for the cryptography version before attempting to use it. ([243](https://github.com/googleapis/google-auth-library-python/pull/243))

- Added `cryptography`-based RSA signer and verifier. ([185](https://github.com/googleapis/google-auth-library-python/pull/185))
- Added `google.oauth2.service_account.IDTokenCredentials`. ([234](https://github.com/googleapis/google-auth-library-python/pull/234))
- Improved documentation around ID Tokens ([224](https://github.com/googleapis/google-auth-library-python/pull/224))

- Added ``google.oauth2.credentials.Credentials.from_authorized_user_file`` ([226](https://github.com/googleapis/google-auth-library-python/pull/#226))
- Dropped direct pyasn1 dependency in favor of letting ``pyasn1-modules`` specify the right version. ([230](https://github.com/googleapis/google-auth-library-python/pull/#230))
- ``default()`` now checks for the project ID environment var before warning about missing project ID. ([227](https://github.com/googleapis/google-auth-library-python/pull/#227))
- Fixed the docstrings for ``has_scopes()`` and ``with_scopes()``. ([228](https://github.com/googleapis/google-auth-library-python/pull/#228))
- Fixed example in docstring for ``ReadOnlyScoped``. ([219](https://github.com/googleapis/google-auth-library-python/pull/#219))
- Made ``transport.requests`` use timeouts and retries to improve reliability. ([220](https://github.com/googleapis/google-auth-library-python/pull/#220))

- Excluded compiled Python files in source distributions. ([215](https://github.com/googleapis/google-auth-library-python/pull/#215))
- Updated docs for creating RSASigner from string. ([213](https://github.com/googleapis/google-auth-library-python/pull/#213))
- Use ``six.raise_from`` wherever possible. ([212](https://github.com/googleapis/google-auth-library-python/pull/#212))
- Fixed a typo in a comment ``seconds`` not ``sections``. ([210](https://github.com/googleapis/google-auth-library-python/pull/#210))