Use hash for cipher config, not Config object

- Config object was just acting as a hash anyway, plus, it was holding
  all options for all ciphers. This means that there is always
  irrelevant config information being passed around.
- Config object was designed to work with Wixy.encrypt and Wixy.decrypt,
  but the options properly belong to the cipher, not the factory
  methods.
Remove Config class

- Remove references to class
- Move cipher-management code from Config to Ciphers