sequences.extras: Add {2,3}nested-each/map combinators
sequences.extras: Add {2,3}nested-each/map combinators

tgunr/factor,factor/factor,factor/factor,mrjbq7/factor,mrjbq7/factor,tgunr/factor,mrjbq7/factor,factor/factor,factor/factor,mrjbq7/factor,mrjbq7/factor,tgunr/factor,tgunr/factor,tgunr/factor,factor/factor,tgunr/factor,factor/factor,mrjbq7/factor