Add support for Arduino Nano 33 IoT (SAMD) (#5)

* fix compilation errors

* add support for Nano 33 IoT

* bump up version, update link in README.md

examples/nano33iot/nano33iot.ino

@@ -0,0 +1,52 @@
+#include <WiFiNINA.h>
+#include <ArduinoHA.h>
+
+#define LED_PIN         9
+#define BROKER_ADDR     IPAddress(192,168,0,17)
+#define WIFI_SSID       "MyNetwork"
+#define WIFI_PASSWORD   "MyPassword"
+
+WiFiClient client;
+HADevice device;
+HAMqtt mqtt(client, device);
+HASwitch led("led", false, mqtt); // you can use custom name in place of "led"
+
+void onSwitchStateChanged(bool state, HASwitch* s)
+{
+    digitalWrite(LED_PIN, (state ? HIGH : LOW));
+}
+
+void setup() {
+    Serial.begin(9600);
+    Serial.println("Starting...");
+
+    // Unique ID must be set!
+    byte mac[WL_MAC_ADDR_LENGTH];
+    WiFi.macAddress(mac);
+    device.setUniqueId(mac, sizeof(mac));
+
+    pinMode(LED_PIN, OUTPUT);
+    digitalWrite(LED_PIN, LOW);
+
+    // connect to wifi
+    WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
+    while (WiFi.status() != WL_CONNECTED) {
+        Serial.print(".");
+        delay(500); // waiting for the connection
+    }
+    Serial.println();
+    Serial.println("Connected to the network");
+
+    // set device's details (optional)
+    device.setName("Nano 33 IoT");
+    device.setSoftwareVersion("1.0.0");
+
+    // handle switch state
+    led.onStateChanged(onSwitchStateChanged);
+
+    mqtt.begin(BROKER_ADDR);
+}
+
+void loop() {
+    mqtt.loop();
+}