Better support to create pooled caches

[vittoriom]

An infix operator would do the trick, but then we'd have to find a good one. Otherwise, I was thinking at a fake cache level result of a pooled() free function that, combined with the usual >>> composition operator, would actually call the pooled(_) function, through an overloading of the >>> operator. But that's also quite weird.

Other options?

[vittoriom]

@esad