Remember last window position/size

[Poopooracoocoo]

Came here from Veloren, a free open-source voxel game. Its launcher, Airshipper, uses Iced which handles winit so I came here.

https://github.com/rust-windowing/winit/issues/941 seems to be relevant.

It's default behaviour on windowed operating systems and one can expect this behaviour by default. It'd be a lot easier on other devs :)