Support using TOML instead of JSON for the input files

[Conan-Kudo]

This is an interesting specification, but JSON is hard for people to write well, and it's not easy for people to read either. It seems the data you want to express can all be done through TOML, so would you consider adding support for that as an alternative to JSON?

[ikeycode]

So the JSON is intended for a universally readable file that we ensure is valid by schema, I don't expect the input format to always be JSON, I'd assume most folks would produce JSON as a subset of some other mechanism.

With that said I'm still happy to add a gated optional toml parser to the crate.