Add support for MemoizeExpiring

[InventivetalentDev]

Adds MemoizeExpiring decorator to support auto-clearing memoized values after a defined duration.
(Also partially implements #13)

@MemoizeExpiring(5000)
public getDataForSomeTime() {
    // do some expensive operation to get data
    return data;
}

[darrylhodgins]

Thanks for the PR, @InventivetalentDev :)