Port to TFT displays

[cgreening]

At the moment the rendering is fairly generic but only ePaper displays are supported - it would be cool to add support for TFT displays and show color ebooks.

[martinberlin]

I recommend to take a look in this component: https://github.com/lovyan03/LovyanGFX
It has support for many displays and it's nicely build. Maybe a good idea will be to have a base class Display that will have all the required methods to draw and it can be initialized either with EPDiy or with another class, so you don't need to add too many changes in the existing code. But even like that it looks like a fairly complicated task.