request zip/zip_longest functionality

Hi, good to see more Python like functions in c++.

Is it possible to have zip and zip_longest use a single iterator over an arbitrary number of containers that are only known at runtime? Just like in Python when unpacking a list of lists? It would really be helpful for me.

[ryanhaining]

I've been thinking about how to go about this and can't come up with a great way to deal with references other than std::reference_wrapper. That's likely what I'll end up using.

Nice. But euh, why do you hesitate using such an approach?