Added a DNSServer library

libraries/DNSServer/examples/DNSServer/DNSServer.ino

@@ -0,0 +1,28 @@
+#include <ESP8266WiFi.h>
+#include <DNSServer.h>
+
+const byte DNS_PORT = 53;
+IPAddress apIP(192, 168, 1, 1);
+DNSServer dnsServer;
+
+void setup() {
+  WiFi.mode(WIFI_AP);
+  WiFi.softAPConfig(apIP, apIP, IPAddress(255, 255, 255, 0));
+  WiFi.softAP("DNSServer example");
+
+  // modify TTL associated  with the domain name (in seconds)
+  // default is 60 seconds
+  dnsServer.setTTL(300);
+  // set which return code will be used for all other domains (e.g. sending
+  // ServerFailure instead of NonExistentDomain will reduce number of queries
+  // sent by clients)
+  // default is DNSReplyCode::NonExistentDomain
+  dnsServer.setErrorReplyCode(DNSReplyCode::ServerFailure);
+
+  //start DNS server for a specific domain name
+  dnsServer.start(DNS_PORT, "www.example.com", apIP);
+}
+
+void loop() {
+  dnsServer.processNextRequest();
+}