coroutines shouldnt be passed mutable values

[ammarbinfaisal]

after #26 is done

[ammarbinfaisal]

this was to prevent data races but if we get mutex #47 implemented then do we really need this?

struct LinkedList<T> {
    data: T,
    next: Option<LinkedList<T>>,
    mu: mutex,
}

enum Option<T> {
    Some(T),
    None    
}