added into_* variations for as_object, as_array

[stnma7e]

Allows a the destructuring of a Json type with move semantics.

For example,

let json_value = Json::from_str("{}").unwrap();
let json_object = (|json: Json| {
    // doesn't compile
    json.as_object()
})(json_value);
assert!(json_object.is_some());

if a Json type is passed to a closure, or some other scope block, when trying to destructure it, there is a lifetime conflict. The Json given as a parameter to the closure was moved, but it cannot be moved out of the closure as an Object.

If you replace as_object with into_object, the Object value returned is not a reference, so it can be moved out of the scope.

But this works,

let json_value = Json::from_str("{}").unwrap();
let json_object = (|json: Json| {
    json.into_object()
})(json_value);
assert!(json_object.is_some());

[alexcrichton]

Thanks!