Re-add automatic window resizing

[DarkDefender]

Autoresize is mentioned in the man (5) page, but not implemented yet.

I think this would be a nice to have as sometime you want to keep the current zoom/position when changing images.

[eXeC64]

This is something I clumsily took out during the raw X11/Wayland refactor as I felt far too lazy to implement proper window resizing with staying centred vs top-left-corner being fixed, etc.

It's only useful when imv is floating, and since its target audience is tiling window manager users, this hasn't been a priority. This can go back in, but it probably won't happen in 4.0 or 4.1.

[eXeC64]

I'm removing it from the man page for now to prevent confusion: ecc58e5

[DarkDefender]

Aha, I thought this was for allowing the user to keep the x,y position and/or zoom level between image changes.

So if I had a zoom of 115%, and the x and y viewport position with some arbitrary value, they would not be reset. So if you are looking at a sequence of images, the viewport would not recenter or rescale on image change.

[DarkDefender]

Perhaps that behavior could be added as new modes for scaling and initial_pan? So:
scaling = preserve so something... 🤔