Google-auth

- Added ``google.auth.credentials.AnonymousCredentials``. ([206](https://github.com/googleapis/google-auth-library-python/pull/#206))
- Updated the documentation to link to the Google Cloud Platform Python setup guide ([204](https://github.com/googleapis/google-auth-library-python/pull/#204))

- ``google.oauth.credentials.Credentials`` now correctly inherits from ``ReadOnlyScoped`` instead of ``Scoped``. ([200](https://github.com/googleapis/google-auth-library-python/pull/#200))

- Added ``service_account.Credentials.project_id``. ([187](https://github.com/googleapis/google-auth-library-python/pull/#187))
- Move read-only methods of ``credentials.Scoped`` into new interface ``credentials.ReadOnlyScoped``. ([195](https://github.com/googleapis/google-auth-library-python/pull/#195), [196](https://github.com/googleapis/google-auth-library-python/pull/#196))
- Make ``compute_engine.Credentials`` derive from ``ReadOnlyScoped`` instead of ``Scoped``. ([195](https://github.com/googleapis/google-auth-library-python/pull/#195))
- Fix App Engine's expiration calculation ([197](https://github.com/googleapis/google-auth-library-python/pull/#197))
- Split ``crypt`` module into a package to allow alternative implementations. ([189](https://github.com/googleapis/google-auth-library-python/pull/#189))
- Add error message to handle case of empty string or missing file for `GOOGLE_APPLICATION_CREDENTIALS` ([188](https://github.com/googleapis/google-auth-library-python/pull/#188))

- Fixed a bug where the Cloud SDK executable could not be found on Windows, leading to project ID detection failing. ([179](https://github.com/googleapis/google-auth-library-python/pull/#179))
- Fixed a bug where the timeout argument wasn't being passed through the httplib transport correctly. ([175](https://github.com/googleapis/google-auth-library-python/pull/#175))
- Added documentation for using the library on Google App Engine standard. ([172](https://github.com/googleapis/google-auth-library-python/pull/#172))
- Testing style updates. ([168](https://github.com/googleapis/google-auth-library-python/pull/#168))
- Added documentation around the oauth2client deprecation. ([165](https://github.com/googleapis/google-auth-library-python/pull/#165))
- Fixed a few lint issues caught by newer versions of pylint. ([166](https://github.com/googleapis/google-auth-library-python/pull/#166))

- Fixed a bug in the clock skew accommodation logic where expired credentials could be used for up to 5 minutes. ([158](https://github.com/googleapis/google-auth-library-python/pull/158))

Milestone release for v1.0.0.