Add facility to update display firmware

[DanNixon]

This is essentially uploading a file from the editor to the display from an SD card on the Arduino.

This should also be able to work from anything that can provide buffered data (e.g. network, bluetooth), it would be worth making this as general purpose as possible.

(itead/ITEADLIB_Arduino_Nextion@f5e38b5)

[giovanne123]

Would be realy nice to have the possibility to upload new tft file from ESP32 to the nextion display directly via Webserver or similiar.

Like in the official itead link you posted or like this https://github.com/Nredor/ESPNexUpload/blob/master/examples/UploadServer/UploadServer.ino

Don't know if you will update/maintain your library...

[DanNixon]

Sorry, but as the readme states I no longer use these displays so have no reason to maintain this library.