add WiFi Event example

libraries/ESP8266WiFi/examples/WiFiClientEvents/WiFiClientEvents.ino

@@ -0,0 +1,48 @@
+/*
+ *  This sketch shows the WiFi event usage
+ *
+ */
+
+#include <ESP8266WiFi.h>
+
+const char* ssid     = "your-ssid";
+const char* password = "your-password";
+
+
+void WiFiEvent(WiFiEvent_t event) {
+    Serial.printf("[WiFi-event] event: %d\n", event);
+
+    switch(event) {
+        case WIFI_EVENT_STAMODE_GOT_IP:
+            Serial.println("WiFi connected");
+            Serial.println("IP address: ");
+            Serial.println(WiFi.localIP());
+            break;
+        case WIFI_EVENT_STAMODE_DISCONNECTED:
+            Serial.println("WiFi lost connection");
+            break;
+    }
+}
+
+void setup() {
+    Serial.begin(115200);
+
+    // delete old config
+    WiFi.disconnect(true);
+
+    delay(1000);
+
+    WiFi.onEvent(WiFiEvent);
+
+    WiFi.begin(ssid, password);
+
+    Serial.println();
+    Serial.println();
+    Serial.println("Wait for WiFi... ");
+}
+
+
+void loop() {
+    delay(1000);
+}
+