cartesian - 

Memory-efficient Cartesian products on heterogeneous collections.

This module is a proof-of-concept to propose memory-efficient views on collections.

This is a specific alternative to combinations, that focuses only highly efficient Cartesian products between collections of different types.

Collection[Int] X Collection[String] -> Collection[(Int,String)]

However, in Nit, there in no native tuple type. So we need a first building block, a pair.