Add Memoize

[clitetailor]

This is convenient when you need to lazily compute a function. There's one problem, If the compute function takes a lot of time to process, it will lock the whole map until it finish.

[pablodz]

Found this fork: https://github.com/arp242/zcache

[arp242]

@pablodz I'm glad you found my fork useful! But commenting on tons of (old) PRs isn't too brilliant, especially when the patches (like this one) aren't even included in the fork.