Cow and ValueRef

[BrandonDyer-Disney]

I understand that sometimes serde_json can't guarantee it'll be able to give a &str because the representation may contain escape characters, but we can typically get around this using Cow.

The same way I can do this with a struct:

#[derive(Deserialize)]
struct MyStruct<'a> {
    #[serde(borrow)]
    some_str: Cow<'a, str>,
}

it would be nice to have the same thing for Value.

// Owned
enum Value {
    Null,
    Bool(bool),
    Number(Number),
    String(String),
    Array(Vec<Value>),
    Object(Map<String, Value>),
}

// Borrowed
enum ValueRef<'a> {
    Null,
    Bool(bool),
    Number(Number),
    String(Cow<'a, str>),
    Array(Vec<ValueRef<'a>>),
    Object(Map<Cow<'a, str>, ValueRef<'a>>),
}