Added support for reporting for freeHeap via MQTT.

src/mqtt.cpp

@@ -69,3 +69,11 @@ void mqtt_loop() {
     mqtt_client.loop();
   }
 }
+
+void mqtt_publish(const char* topic, int number) {
+    char t[127];
+    sprintf(t, MQTT_TOPIC "%s", topic);
+    char b[32];
+    sprintf(b, "%d", number);
+    mqtt_client.publish(t, b);
+}