Added a basic WiFi UDP client example (#114)

* Added a basic WiFi UDP client example: a sketch that sends random bytes over udp.

* Updated udp example and included Python and Ruby UDP servers.

libraries/WiFi/examples/WiFiUDPClient/WiFiUDPClient.ino

@@ -0,0 +1,75 @@
+/*
+ *  This sketch sends random data over UDP on a ESP32 device
+ *
+ */
+#include <WiFi.h>
+#include <WiFiUdp.h>
+
+// WiFi network name and password:
+const char * networkName = "your-ssid";
+const char * networkPswd = "your-password";
+
+//IP address to send UDP data to:
+// either use the ip address of the server or 
+// a network broadcast address
+const char * udpAddress = "192.168.0.255";
+const int udpPort = 3333;
+
+//Are we currently connected?
+boolean connected = false;
+
+//The udp library class
+WiFiUDP udp;
+
+void setup(){
+  // Initilize hardware serial:
+  Serial.begin(115200);
+  
+  //Connect to the WiFi network
+  connectToWiFi(networkName, networkPswd);
+}
+
+void loop(){
+  //only send data when connected
+  if(connected){
+    //Send a packet
+    udp.beginPacket(udpAddress,udpPort);
+    udp.printf("Seconds since boot: %u", millis()/1000);
+    udp.endPacket();
+  }
+  //Wait for 1 second
+  delay(1000);
+}
+
+void connectToWiFi(const char * ssid, const char * pwd){
+  Serial.println("Connecting to WiFi network: " + String(ssid));
+
+  // delete old config
+  WiFi.disconnect(true);
+  //register event handler
+  WiFi.onEvent(WiFiEvent);
+  
+  //Initiate connection
+  WiFi.begin(ssid, pwd);
+
+  Serial.println("Waiting for WIFI connection...");
+}
+
+//wifi event handler
+void WiFiEvent(WiFiEvent_t event){
+    switch(event) {
+      case SYSTEM_EVENT_STA_GOT_IP:
+          //When connected set 
+          Serial.print("WiFi connected! IP address: ");
+          Serial.println(WiFi.localIP());  
+          //initializes the UDP state
+          //This initializes the transfer buffer
+          udp.begin(WiFi.localIP(),udpPort);
+          connected = true;
+          break;
+      case SYSTEM_EVENT_STA_DISCONNECTED:
+          Serial.println("WiFi lost connection");
+          connected = false;
+          break;
+    }
+}