Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/@python2/sha.pyi

@@ -0,0 +1,10 @@
+class sha(object):
+    def update(self, arg: str) -> None: ...
+    def digest(self) -> str: ...
+    def hexdigest(self) -> str: ...
+    def copy(self) -> sha: ...
+
+def new(string: str = ...) -> sha: ...
+
+blocksize: int
+digest_size: int