Hashing function BLAKE2 - both blake2s and blake2b

Currently Sesam DTL supports hashing function `murmurhash3`. This is known as a fairly good and performant hashing function, but it has quite a bit of collisions still. A cryptographic hashing function will not have any collisions, or it will be "extremely difficult" when the crypto hash function is any good.

The BLAKE2 "B" and "S" variants are very efficient, the "blake2s" is similar in performance as "sha1" but vastly superior security (less collisions likely).

Both "blake2s" and "blake2b" are available in the Python3 standard "hashlib" as well.
See also:
- https://docs.python.org/3/library/hashlib.html#hashlib.blake2s
- https://en.wikipedia.org/wiki/BLAKE_(hash_function)#BLAKE2