* https://hackaday.com/2015/09/18/transparent-esp8266-wifi-to-serial-bridge/
  * https://github.com/LowPowerLab/DualOptiboot

documentation on optiboot

  * https://github.com/Optiboot/optiboot/wiki/HowOptibootWorks
  * https://forum.arduino.cc/index.php?topic=299046.0
  * https://github.com/sparkfun/tomatoless_boots/blob/master/tomatoless.device.nut
  * https://www.avrfreaks.net/forum/uploading-sketch-arduino-procedure



theoretically, we should be able to issue STK_PROG_PAGE commands through uart to upload firmware