Support comment retention in fnox.toml (in fnox set)

[colelawrence]

I like to put all of my documentation directly into these TOML files so that other people can understand and read the like TOML files where things are defined to understand how they're linked. For now, my workaround is defining an fnox.README.md file.

[theutz]

I think this is a good point. It seems like fnox edit preserves comments, so if you're not worried about a colleague wiping your secrets out, that might also do as a workaround.

[colelawrence]

I can confirm that fnox edit preserves comments! That is working great.

[colelawrence]

I've added some comment preservation tests that are failing that can be observed in colelawrence@ff5d097 - I'd be happy to open as a PR