Finish Python 3 hashlib stub (#179)

stdlib/3/hashlib.pyi

@@ -1,11 +1,17 @@
 # Stubs for hashlib
 
-# NOTE: These are incomplete!
-
 from abc import abstractmethod, ABCMeta
-import typing
+from typing import AbstractSet
 
 class Hash(metaclass=ABCMeta):
+    digest_size = ...  # type: int
+    block_size = ...  # type: int
+
+    # [Python documentation note] Changed in version 3.4: The name attribute has
+    # been present in CPython since its inception, but until Python 3.4 was not
+    # formally specified, so may not exist on some platforms
+    name = ...  # type: str
+
     @abstractmethod
     def update(self, arg: bytes) -> None: ...
     @abstractmethod
@@ -23,3 +29,12 @@ def sha384(arg: bytes = ...) -> Hash: ...
 def sha512(arg: bytes = ...) -> Hash: ...
 
 def new(name: str, data: bytes = ...) -> Hash: ...
+
+# New in version 3.2
+algorithms_guaranteed = ...  # type: AbstractSet[str]
+algorithms_available = ...  # type: AbstractSet[str]
+
+# New in version 3.4
+# TODO The documentation says "password and salt are interpreted as buffers of
+# bytes", should we declare something other than bytes here?
+def pbkdf2_hmac(name: str, password: bytes, salt: bytes, rounds: int, dklen: int = ...) -> bytes: ...