Add test/compatibility folder with small servers and clients written in different languages and different libraries to test compatibility.

test/compatibility/python/websockets/README.md

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+# Clients
+
+## ws
+
+```
+$ ws connect ws://127.0.0.1:8765
+Type Ctrl-D to exit prompt...
+Connecting to url: ws://127.0.0.1:8765
+> ws_connect: connected
+Uri: /
+Handshake Headers:
+Connection: Upgrade
+Date: Sat, 08 Jun 2019 16:43:29 GMT
+Sec-WebSocket-Accept: kPCNwGa97y+7NWdAvHi/7/rA8AE=
+Sec-WebSocket-Extensions: permessage-deflate; server_max_window_bits=15; client_max_window_bits=15
+Server: Python/3.7 websockets/7.0
+Upgrade: websocket
+Received 13 bytes
+ws_connect: received message: > Welcome !
+ws_connect: connection closed: code 1006 reason Abnormal closure
+```
+
+## wscat
+
+```
+$ ./node_modules/.bin/wscat -c ws://127.0.0.1:8765
+connected (press CTRL+C to quit)
+< > Welcome !
+disconnected (code: 1006)
+```

test/compatibility/python/websockets/echo_server.py

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+#!/usr/bin/env python
+
+# WS server example
+
+import asyncio
+import websockets
+
+async def hello(websocket, path):
+    await websocket.send(f"> Welcome !")
+
+    name = await websocket.recv()
+    print(f"< {name}")
+
+    greeting = f"Hello {name}!"
+
+    await websocket.send(greeting)
+    print(f"> {greeting}")
+
+start_server = websockets.serve(hello, 'localhost', 8765)
+
+asyncio.get_event_loop().run_until_complete(start_server)
+asyncio.get_event_loop().run_forever()