The current implementation contains two potential security
vulnerabilities. The Redis key assigned by Redbird could be manipulated
to potentially access other data in Redis and assign it as part of the
user's session information. Values stored in Redis are also being
deserialized using an Erlang function that can execute functions stored
as values.

This change closes those potential security vulnerabilities by
cryptographically signing the Redis key used by Redbird and by using a
deserialization function that safely handles Erlang terms including
functions. When a user places a key-value in Redis via Redbird, Redbird
generates a key, signs it, and optionally prepends the namespace. When
accessing the key from Redis, Redbird verifies the key, rejects keys
that have been tampered with, and safely deserializes the stored Erlang
terms. Likewise, Redbird only permits deletion of keys that are valid.

Introduce a Value module that handles the serialization and
deserialization of the value store in Redis by Redbird.