Interactive, piecewise, on-demand rendering

[jonnor]

When using imgflo interactively, it is primarily possible to see the entire output in full resolution for relatively small images (depending on screen size). For many cases involving large images, on either looks at a part of the image or is looking at a scaled-down version of it.

It should be possible to render only that which is needed for display, and on-demand and in multiple pieces (for user feedback).
This would need additions in the HTTP /process API to take scale/bounding boxes.

The client-side logic here might become pretty complicated, so it should probably be a library.