Added operator == to compare JsonVariant and strings (issue #402)

examples/ProgmemExample/ProgmemExample.ino

@@ -39,9 +39,14 @@ void setup() {
   // JsonBuffer.
   root["sensor"] = F("gps");
 
+  // You can compare the content of a JsonVariant to a Flash String
+  if (root["sensor"] == F("gps")) {
+    // ...
+  }
+
 #else
 
-#warning PROGMEM is only supported on AVR architecture
+#warning PROGMEM is not supported on this platform
 
 #endif
 }

examples/StringExample/StringExample.ino

@@ -48,6 +48,11 @@ void setup() {
   // WARNING: the content of the String will be duplicated in the JsonBuffer.
   root[String("sen") + "sor"] = String("gp") + "s";
 
+  // You can compare the content of a JsonObject with a String
+  if (root["sensor"] == sensor) {
+    // ...
+  }
+
   // Lastly, you can print the resulting JSON to a String
   String output;
   root.printTo(output);