Previously there was a possibility that Session to WebSocket mapping was
leaked if keyspace notifications were not enabled in Redis.
To resolve this the RedisHttpSessionConfiguration now ensures that Redis
is configured to enable Keyspace notifications.
Fixes gh-76 gh-81
Redis key expiration has no guarantees of when the expired key is
actually removed. In some instances, it is necessary to clean up resources
as soon as the sessione expires. For example, when an HTTP Session expires
we must ensure that the associated Web Socket sessions are closed.
Sessions are now mapped to their expiration times and a background task
is used to clean up the sessions as they expire.
Fixes gh-59
This provides a better separation for consumers of the API. Most users are
likely not interested in checking to see if a session is expired so they
can focus on the Session API.
Fixes#28
