This code is meant to run on an Adafruit Trinket M0 and implement the MQTT protocol using a esp8266 running stock (AT-command) firmware and communicating over UART. This is NOT meant to run ON an esp8266.
This is currently very much a work in progress. The basic functionality is there, but not in a state that can be just used without some effort. I think this code is more readable than other mqtt libraries I've seen, so if you are trying to understand the mqtt protocol, reading through it might help.