add size to Siblings

[kczimm]

Add the file size to the Siblings struct.

[McPatate]

lgtm, @Narsil ?

[Narsil]

This would need to be done to both sync/async parts.

I'd rather make it easer for everyone to get exactly what they want. This is what info_request() should get you.
With info_request users can get exactly what they want (including the size or not, or any other information).

I think maybe expanding/showcasing this might be more useful than modifying this for everyone.
We should probably add a link within info too.