PUBSUB MQTT library used in home automation - esp8266 nodemcu io.adafruit.com broker, but using the MQTT PubSub client library.
17.12.2016: Ricardo Timmermann inspired by Andreas Spiess and of course, Ivan Grokhotkov.
Reset device testing IST. When GPIO13 is high it should enter ISR routine. After uploading the code you should HW reset the ESP8266, so it works. There are some issues described by: