Document that ocaml values need to be rooted

[Lupus]

Maybe I've missed this in the documentation, but I didn't realize that storing ocaml::Value somewhere outside of #[ocaml::func] will lead to crashes after OCaml GC disposes the value.

After adding this to my function, things started to work:

let handler = ocaml::Value::from(handler.raw().0);

Perhaps ocaml::Value should be provided with custom Clone implementation that ensures that cloned value is properly rooted.

[Lupus]

Maybe some helper like this needs to be added to the library and documented? 🤔

pub fn ensure_rooted_value(value: ocaml::Value) -> ocaml::Value {
    match value {
        ocaml::Value::Raw(v) => unsafe { ocaml::Value::Root(ocaml::root::Root::new(v)) },
        ocaml::Value::Root(_) => value,
    }
}

[zshipko]

Adding something like that seems reasonable to me. Could you open a PR for this?

[Lupus]

Yeah, sure. Will do.