(apple ssl) model write method after the OpenSSL one for consistency

More test code for #140.

test/compatibility/python/websockets/echo_server_ssl.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python
+
+# WS server example
+
+import asyncio
+import os
+import pathlib
+import ssl
+import websockets
+
+
+async def echo(websocket, path):
+    msg = await websocket.recv()
+    print(f'Received {len(msg)} bytes')
+    await websocket.send(msg)
+
+ssl_context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
+ssl_context.load_cert_chain('trusted-server-crt.pem',
+                            'trusted-server-key.pem')
+
+print('Serving on localhost:8766')
+host = os.getenv('BIND_HOST', 'localhost')
+start_server = websockets.serve(echo, host, 8766, max_size=2 ** 30, ssl=ssl_context)
+
+asyncio.get_event_loop().run_until_complete(start_server)
+asyncio.get_event_loop().run_forever()