Replaced printTo() with serializeJson()

* Added `serializeJson()` and `serializeJsonPretty()`
* Added `measureJson()` and `measureJsonPretty()`
* Removed `printTo()` and `prettyPrintTo()`
* Removed `measureLength()` and `measurePrettyLength()`

examples/JsonUdpBeacon/JsonUdpBeacon.ino

@@ -72,11 +72,11 @@ void loop() {
   Serial.print(remoteIp);
   Serial.print(F(" on port "));
   Serial.println(remotePort);
-  root.printTo(Serial);
+  serializeJson(root, Serial);
 
   // Send UDP packet
   udp.beginPacket(remoteIp, remotePort);
-  root.printTo(udp);
+  serializeJson(root, udp);
   udp.println();
   udp.endPacket();