Bebleo-smtpd-fixture

Final release as bebleo_smtpd_fixture before becoming smtpdfix.

- Adds deprecation warning to the fixture letting developers know that if by chance they're using bebelo_smtpd_fixture they should move to smtpdfix

Adds support for enforcing authentication. Specific changes include:

- Adds a changelog.
- Adds support for `.env` files with `python-dotenv`.
- Enforces encryption on AUTH methods that require it.
- Corrects bug that prevented cancelling authentication with the LOGIN mechanism by sending a * and updates error message to match [RFC4954 - SMTP Service Extension for Authentication](https://www.ietf.org/rfc/rfc4954.txt).
- Corrects bug that caused the fixture hang on windows if certificates were not found in the path specified by the `SMTPD_SSL_CERTS_PATH`.
- Ensures that the session is authenticated when the `SMTPD_ENFORCE_AUTH` environment flag is set to `True` before processing DATA, MAIL, RCPT commands.

This version adds authentication and encryption to the fixture. Specifically:

+ SSL/TLS is now support and certificates are supplied out-of-the box if logging in using 127.0.0.1 or localhost as the address
+ Authentication now supports CRAM-MD5, PLAIN, and LOGIN mechanisms.

Version 0.2.0 implements authentication for the fixture to simulate a more realistic environment for testing.