Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/asyncio/protocols.pyi

@@ -0,0 +1,27 @@
+import sys
+from asyncio import transports
+from typing import Optional, Tuple
+
+class BaseProtocol:
+    def connection_made(self, transport: transports.BaseTransport) -> None: ...
+    def connection_lost(self, exc: Optional[Exception]) -> None: ...
+    def pause_writing(self) -> None: ...
+    def resume_writing(self) -> None: ...
+
+class Protocol(BaseProtocol):
+    def data_received(self, data: bytes) -> None: ...
+    def eof_received(self) -> Optional[bool]: ...
+
+if sys.version_info >= (3, 7):
+    class BufferedProtocol(BaseProtocol):
+        def get_buffer(self, sizehint: int) -> bytearray: ...
+        def buffer_updated(self, nbytes: int) -> None: ...
+
+class DatagramProtocol(BaseProtocol):
+    def datagram_received(self, data: bytes, addr: Tuple[str, int]) -> None: ...
+    def error_received(self, exc: Exception) -> None: ...
+
+class SubprocessProtocol(BaseProtocol):
+    def pipe_data_received(self, fd: int, data: bytes) -> None: ...
+    def pipe_connection_lost(self, fd: int, exc: Optional[Exception]) -> None: ...
+    def process_exited(self) -> None: ...