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/emu

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+# linux script to compile&run arduinoWebSockets in a mock environment
+
+if [ -z "$ESP8266ARDUINO" ]; then
+    echo "please set ESP8266ARDUINO env-var to where esp8266/arduino sits"
+    exit 1
+fi
+
+set -e
+
+where=$(pwd)
+
+cd $ESP8266ARDUINO/tests/host/
+
+make -j FORCE32=0 \
+    ULIBDIRS=../../libraries/Hash/:~/dev/proj/arduino/libraries/arduinoWebSockets \
+    ${where}/WebSocketServerHooked
+
+valgrind ./bin/WebSocketServerHooked/WebSocketServerHooked -b "$@"