Have it take in a cipher init function as an argument.
Remove the confusing `newCipher` method that matched legacy behavior
and returns a Base64Cipher(CFBCipher) -- instead explicitly ask for
that in the uses.
During the upcoming encoded session refactor, AES GCM is ideal
to use as the Redis (and other DB like stores) encryption wrapper
around the session because each session is encrypted with a
distinct secret that is passed by the session ticket.
All Encrypt/Decrypt Cipher implementations will now take
and return []byte to set up usage in future binary compatible
encoding schemes to fix issues with bloat encrypting to strings
(which requires base64ing adding 33% size)
