Add Weak references

[spotandjake]

When working in a garbage collected language sometimes it is nice to have a little bit more control over memory management a common prototype for this is WeakReferences basically references to objects that do not prevent the value from being freed.

I am thinking we have a simple WeakRef type with the operation getValue which will return an option depending on if the object has been freed or not already to maintain program safety.

Weak references have many use cases one such use case is for breaking cyclic chains in the gc which would otherwise fail to be collected.