Add suport for non-square pixel modes

[steffest]

Add suport for e.g. hires and interlaced images.

[jayenne]

oooh I'd like this too. I was an Amiga game artist in the 80/90's and most of my own work was hiRes 16colour and would love to work this way again... if only to see how much I have missed it, ...and degraded my own abilities since 🤣