Add RedisClientConfiguration class. With it you may configure your client via URL or unix_socket_path.
Add turnstile module providing a special case turnstile_client_factory, which can be used as a drop in turnstile.redis_client entrypoint with the
turnstile rate limiting middleware.
Explicitly write the redis. namespace in the default settings dict keys.
Support a REDIS_KEY environment variable to make picking up vars from
providers like REDISTOGO and REDISCLOUD easier.
Make sure that DB and MAX_CONNECTIONS are ints.
Initial release.