This format can store an arbitrary number of resolutions of the image in one file.
At the moment we're just doing two though, the first one for icons (32x32), the second for images (full size).

I'm not 100% satisfied with this code, but it does work.

Well actually I converted them from the original JPG / PNG files, but the result is the same.

I think this is a bit more elegant.

Removed some newlines which I felt didn't belong.
Renamed count to length when talking about (width * height), because that's what I call it elsewhere in the code too, and count refers to the amount of images in a BIP file.
Updated an assert message that I forgot to update earlier.
Changed how the data dictionary is used, so now icon_size and icon_pixels are set on its creation, and only overwritten in if the icon needed resizing.

I did the same for the loader and I like to be consistent.

Functionally the same but more explicit.

Just to show that previews can be used as icons now.

This code is a bit opaque otherwise.

Interestingly, the loader seems to support BIP2 files with only one resolution, even though it expects two.
I haven't tested it, but just reading the code, that's how it probably works.