Re-organize directory structure (#4971)

See discussion in #2491

Co-authored-by: Ivan Levkivskyi <ilevkivskyi@dropbox.com>

stdlib/@python2/hashlib.pyi

@@ -0,0 +1,28 @@
+from typing import Tuple, Union
+
+_DataType = Union[str, unicode, bytearray, buffer, memoryview]
+
+class _hash(object):  # This is not actually in the module namespace.
+    name: str
+    block_size: int
+    digest_size: int
+    digestsize: int
+    def __init__(self, arg: _DataType = ...) -> None: ...
+    def update(self, arg: _DataType) -> None: ...
+    def digest(self) -> str: ...
+    def hexdigest(self) -> str: ...
+    def copy(self) -> _hash: ...
+
+def new(name: str, data: str = ...) -> _hash: ...
+def md5(s: _DataType = ...) -> _hash: ...
+def sha1(s: _DataType = ...) -> _hash: ...
+def sha224(s: _DataType = ...) -> _hash: ...
+def sha256(s: _DataType = ...) -> _hash: ...
+def sha384(s: _DataType = ...) -> _hash: ...
+def sha512(s: _DataType = ...) -> _hash: ...
+
+algorithms: Tuple[str, ...]
+algorithms_guaranteed: Tuple[str, ...]
+algorithms_available: Tuple[str, ...]
+
+def pbkdf2_hmac(name: str, password: str, salt: str, rounds: int, dklen: int = ...) -> str: ...