Changed

• set_keylog(None) will no longer trigger monkey patching, making it easier to use it
  conditionally.
• Updated documentation to show how to support SSLKEYLOGFILE.
• Document that some methods don't work with TLS v1.3 as the values they are meant to return
  don't exist anymore in TLS v1.3.

Fixed

• Fix tests when TLS v1.3 is enabled by default.