Creates an encrypted cookie storage engine. Accepts the following options:

:key - The secret key to encrypt the session cookie. Must be a byte array of
       exactly 16 bytes. If no key is provided then a random key will be
       generated. Note that in that case a server restart will invalidate all
       existing session cookies.

:readers - A map of data readers used to read the serialized edn from the
           cookie. For writing, ensure that each data type has a key in the
           clojure.core/print-method or clojure.core/print-dup multimethods.