* Add cryptography backend for get_certificate.
* Add changelog.
* Use short names (if possible).
* Adjust version (to behave as pyOpenSSL).
* Work around bugs (needed for cryptography 1.2.3).
* Don't run cryptography backend tests for CentOS 6.
* Bump cryptography requirement to 1.6 or newer.
Otherwise, signature_algorithm_oid isn't there, either.
* Simplify requirement text.
* CentOS 6 has cryptography 1.9, so we still need to block.
* Add auto-detect test.
* Improve YAML.
