St7701 cached

[AndrewCapon]

This adds a new subclass ST7701Cached that uses a small cache in pico ram to drive the underlying ST7701 class.

This allows freeing up lots of lovely pico ram but with some disadvantages:

Due to the reduced memory use the normal Update where the display is updated behind the current scanline is no longer used, so if you run with a single back buffer then you will see some flicker. You can run with two back buffers then you do have the speed of the psram to deal with when keeping them in sync.

Some example code using it: https://github.com/AndrewCapon/presto-cached-examples

[Slion]

That looks interesting but I'm not sure I understand how it works.
Ok, I found the issue and will do some reading.

[AndrewCapon]

If you have any questions just ask.