Serializers for cookies
Update MessageVerifier to use a Serializer

You can specify your own serializer
Pseudo-random key generator
MessageEncryptor
Update Cookie store with encryption and signing options
Don't need this anymore
Merge pull request #72 from scrogson/encrypted_cookies

Add MessageEncryptor
Extract serialization from message verifier/encrptor
Move Crypto stuff to Plug.Crypto
Make all encryption arguments explicit
Refactor KeyGenerator
Use sha256 by default
Allow keys to be cached
Move secret_key_base to the connection
Release v0.8.0
Start v0.8.1-dev