Pyramid-redis

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.

[turnstile]: https://github.com/klmitch/turnstile

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.