Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/email/encoders.pyi

@@ -0,0 +1,6 @@
+from email.message import Message
+
+def encode_base64(msg: Message) -> None: ...
+def encode_quopri(msg: Message) -> None: ...
+def encode_7or8bit(msg: Message) -> None: ...
+def encode_noop(msg: Message) -> None: ...