Should native use `Yojson.Safe`?

[jchavarri]

We had a recent case where melange-json would fail at runtime trying to parse ints that overflow ocaml representation.

@andreypopp I guess there were reasons why Yojson.Basic was chosen. What are the tradeoffs? Could melange-json move to use Yojson.Safe potentially?

[andreypopp]

I think it's a good idea.