PNG region support for load_sprite

[Gadgetoid]

I've now- as of the latest CI build over at #8 - added the ability to load a portion of a PNG image into a sprite. You can use this by supplying a four-tuple third argument to load_sprite, containing an X/Y offset and a width and height.

eg:

display.load_sprite("pim-logo.png", LOGOSUB1_INDEX, (0, 0, 32, 32))
display.load_sprite("pim-logo.png", LOGOSUB2_INDEX, (32, 0, 32, 32))
display.load_sprite("pim-logo.png", LOGOSUB3_INDEX, (0, 32, 32, 32))
display.load_sprite("pim-logo.png", LOGOSUB4_INDEX, (32, 32, 32, 32))

You can usually find the latest cutting-edge firmware by going here - https://github.com/pimoroni/picovision/actions/workflows/micropython.yml

And finding whatever feature branch is being worked upon, in this case the instances of "PicoVector Bring-up", just click the latest and scroll down to find the smaller, non-examples .uf2.