Port to Raspberry Pi Pico W core

Add support for the onboard WiFi chip on the Raspberry Pi Pico W
(RP2040 based ) board using the arduino-pico Arduino core at
https://github.com/earlephilhower/arduino-pico

The PicoW WiFi stack is a mashup of the ESP8266 and ESP32 cores, so
only minimal changes were required.  Defines a new NETWORK_TYPE for
the PicoW.

ESP8266 examples renames to ESP8266_PICO because they all work unmodified
(except for OTA which is handled differently on the Pico)

examples/esp8266_pico/WebSocketServerHooked/ws-testclient.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python3
+
+# python websocket client to test with
+# emulator: server is at ws://127.0.0.1:9080/ws
+# esp8266:  server is at ws:///ws
+# (uncomment the right line below)
+
+#uri = "ws://127.0.0.1:9080/ws"
+uri = "ws://arduinoWebsockets.local/ws"
+
+import websocket
+try:
+    import thread
+except ImportError:
+    import _thread as thread
+import time
+
+def on_message(ws, message):
+    print("message");
+    print(message)
+
+def on_error(ws, error):
+    print("error")
+    print(error)
+
+def on_close(ws):
+    print("### closed ###")
+
+def on_open(ws):
+    print("opened")
+    def run(*args):
+        for i in range(3):
+            time.sleep(1)
+            ws.send("Hello %d" % i)
+        time.sleep(1)
+        ws.close()
+        print("thread terminating...")
+    thread.start_new_thread(run, ())
+
+
+if __name__ == "__main__":
+    websocket.enableTrace(True)
+    ws = websocket.WebSocketApp(uri, on_message = on_message, on_error = on_error, on_close = on_close)
+    ws.on_open = on_open
+    ws.run_forever()