Debug ESP8266
https://blog.squix.org/2016/04/esp8266-offline-debugging-with.html
https://blog.attachix.com/live-debugging-with-open-source-tools-programming-for-esp8266-part-4/
https://github.com/espressif/esp-gdbstub
https://visualgdb.com/tutorials/esp8266/gdbstub/
https://github.com/esp8266/Arduino/issues/384