Publish refactoring (#298)

* factoring of the publishing function
* integration of json publishing to MQTT
* receiving and transcode json messages from mqtt
* replace the TRACE runtime condition by a buildtime one so as to decrease program size
* remove retainFlag parameter not necessary for the moment
* Increase the scope of tests for arduino mega and esp32
* Update arduinojson library to 5.13.3
* add macros to choose between simple or json publishing or both
* differentiate build test for ATmega2560
* correct wrong sprintf definition
* change IDE version for continuous integration
* let default warning level in arduino ide
* correct pins for ESP32
* reorganize user_config

ZsensorDHT.ino

@@ -48,20 +48,20 @@ void MeasureTempAndHum(){
     if (isnan(h) || isnan(t)) {
       trc(F("Failed to read from DHT sensor!"));
     }else{
+      trc(F("Creating DHT buffer"));
+      StaticJsonBuffer<JSON_MSG_BUFFER> jsonBuffer;
+      JsonObject& DHTdata = jsonBuffer.createObject();
       if(h != persistedh || dht_always){
-        trc(F("Sending Hum to MQTT"));
-        trc(h);
-        client.publish(HUM1,String(h).c_str());
+        DHTdata.set("hum", (float)h);
        }else{
         trc(F("Same hum don't send it"));
        }
       if(t != persistedt || dht_always){
-        trc(F("Sending Temp to MQTT"));
-        trc(t);
-        client.publish(TEMP1, String(t).c_str());
+        DHTdata.set("temp", (float)t);
       }else{
         trc(F("Same temp don't send it"));
       }
+      if(DHTdata.size()>0) pub(DHTTOPIC,DHTdata);
     }
     persistedh = h;
     persistedt = t;