Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/secrets.pyi

@@ -0,0 +1,12 @@
+from hmac import compare_digest as compare_digest
+from random import SystemRandom as SystemRandom
+from typing import Optional, Sequence, TypeVar
+
+_T = TypeVar("_T")
+
+def randbelow(exclusive_upper_bound: int) -> int: ...
+def randbits(k: int) -> int: ...
+def choice(seq: Sequence[_T]) -> _T: ...
+def token_bytes(nbytes: Optional[int] = ...) -> bytes: ...
+def token_hex(nbytes: Optional[int] = ...) -> str: ...
+def token_urlsafe(nbytes: Optional[int] = ...) -> str: ...