Update for ESP8266 and latest Arduino board support package

ESP8266 board support package 2.3.0 or later required

Update library.json

Update README.md

Update for Adafruit_GFX setAddrWindow() parameter change

Now works with ESP32 and SD library

Correct 8x8 MCU bug

OK, got the bug nailed this time!

Support loading of SD for other architectures

Plus improved explanatory comments

Update version number

Update library to be Arduino structure compliant