Offset and crop image file via Rust

[swfsql]

The image offsetting and cropping is done via tex primitives. This means the output pdf file is bigger than necessary.
It's better if the program does this and replacing the file itself. Then the TeX template will be simpler, and the output file will be smaller.

For now, the actual file size will have to be passed as information to TeX. But after this issue is resolved, we can treat the zero number (for dimensions) as "all of the remaining". This would make the info files simpler.

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Before closing, needs to deal with the zero dimension (for automatic dimensioning based on the maximum of the required minimum) setting.

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Moved from ancap-ch/from-en#708