Nettle: Added a bunch of proxy functions for the modes.

The modes should now have all the API functions.
Testsuite: Added generic tests of most Ciphers and AEADs.

Validate that the encryption and decryption modes are each others
inverses, and that the AEAD digests generate the same data in both.
Nettle: Release the interpreter for encrypt and decrypt.

Allow other threads to execute when encrypting or decrypting
data larger than 1 KB.
Removed dead code.