Refactor, fixes, add api, tests.

* Change KeyTypeWrapper to EncryptionScheme
* Change OpenPGPWrapper to OpenPGPScheme
* Add missing and standardized crypto API.
* Add delete_key()
* Fix put_key raw so it puts either public or private keys.
* Fix gpg's is_encrypted()
* Fix openpgp's safe callbacks so they return correctly.
* Remove binascii because it generates invalid doc ids.
* Add tests.