Handle nan and inf in von

[Denneisk]

Fixes #3168

Von could stand to have a rewrite. If we do a clean-room rewrite, we can even get rid of the ugly license.

[Vurv78]

Von shouldn't really be used but would be cool if it was done ala qjson if anyone wanted to put in the effort.

[Denneisk]

What do you mean precisely by that?

[thegrb93]

There's plenty of serialization deserialization options. sfs is another. I'd have preferred json, but I don't know if json always handles numbers correctly either. If json works, I'd prefer switching to that.

[thegrb93]

If you want to replace von with sfs, that'd be a good effort too, but we can also just merge this if this works.

[Denneisk]

I'm fine with deprecating von but unfortunately for now it needs to stay for backwards compat with dupes that use it.

If we wanted to be surreptitious about it, we could detour the von serializer to another one and make the von deserializer branch between the new and von. That way there would be no API changes. SFS, for example, can be discriminated by it always starting with a non-printing character when given a table.

[thegrb93]

I don't think sfs data should be mixed in as if it's von. Better to just give users a tool to convert their von to sfs and phase out the von functions.

The problem is once von is fully removed, people will have no idea why their old data stops working.