Nettle: Unified cipher16.H and cipher.H.

Some cleanups to reduce code duplication.

Introduces a new intermediate class Nettle.BlockCipher
intended to hold stuff common to all block ciphers.

Renamed Nettle.Cipher16 to Nettle.BlockCipher16 for clarity.
No need to resolv Builtin function.
Nettle: Moved CBC from a class to a submodule of BlockCipher.

This adds things like Crypto.AES.CBC analogous to Crypto.AES.GCM.
Don't add duplicates to load_authorities response.
Nettle: Moved Buffer from a class to a submodule of BufferedCipher.

This adds things like Crypto.AES.Buffer and Crypto.AES.CBC.Buffer
analogous to Crypto.AES.GCM.
Nettle: Improved typing.

Don't hide the programs for the submodules, they are useful for typing.

Improved type for BufferCipher()->Buffer->`().

Fixes remaining warning in Standards.PEM.
AutoDoc: Fixed some markup bugs in Nettle.
Better key size code for _sprintf.
Move STATE_* constants to Constants to reuse debug code.
AutoDoc: Some more markup fixes for Nettle.
Less random data in the debug output...
Improved the extension debug somewhat.