Added JsonPrintable.prettyPrintTo(Print&)

examples/JsonGeneratorExample/JsonGeneratorExample.ino

@@ -21,6 +21,9 @@ void setup()
     root["data"] = array;
 
     Serial.print(root); // {"sensor":"gps","time":1351824120,"data":[48.756080,2.302038]}
+
+    Serial.println();
+    root.prettyPrintTo(Serial); // same string indented
 }
 
 void loop()