* Fix blake2 binding
Currently calling `hashlib.blake2b` results in the following type errors:
Cannot instantiate abstract class '_BlakeHash' with abstract attributes 'copy', 'digest', 'hexdigest' and 'update'
Missing positional arguments "data", "key", "salt", "person", "fanout", "depth", "leaf_size", "node_offset", "node_depth", "inner_size", "last_node" in call to "_BlakeHash"
* Additional changes to reflect the hashlib implementation
Modifies the type signatures of:
* blake2b
* blake2s
* sha3_224
* sha3_256
* sha3_384
* sha3_512
* shake_128
* shake_256
To reflect the types that are implemented in the standard library.
These should be exposed as `type`s instead of `builtin_function_or_method`s.
e.g.
In [40]: type(hashlib.blake2b)
Out[40]: type
In [41]: type(hashlib.md5)
Out[41]: builtin_function_or_method
* sha3 family of hash functions
* shake variable length hashes that were introduced alongside sha3
* blake2 family of hash functions
* Mark VarLenHash as a private class, since it's not actually exported by hashlib
* Fix typos in my last, and mark hashlib.Hash as a private class since it isn't in the real hashlib
* Update pbkdf2_hmac for Python 3.5
- Use `iterations` instead of `rounds` if running on 3.5
- Change `dklen` to `Optional`
* Use `iterations` instead of `rounds` in 3.4+
