Additional authenticated data can now be specified with the new
aad(Chars) option for encryption and decryption. It is authenticated,
but not encrypted.
This avoids the costly (in terms of space requirements!) conversion of
compact lists of characters to lists of integers, making hashing, HKDF,
encryption, decryption, signing and signature verification an order of
magnitude more efficient (primarily in terms of space, also in time).
This makes library(crypto) suitable to process also very large files.
