Zip generator for comprehensions

[lucioleKi]

This EEP proposes the addition of zip generators with a syntax of && for comprehensions in Erlang. The idea and syntax of zip generators (comprehension multigenerators) was first brought up by EEP-19. Even if the syntax and usages of zip generators proposed by this EEP is mostly the same with EEP-19, the comprehension language of Erlang has undergone many changes since EEP-19 was accepted. With an implementation that is compatible with all existing comprehensions, this EEP defines the behavior of zip generators with more clarification on the compiler's part.