Map calls mapply instead of creating a Mapply directly
added describe tool
minor updates for debug macros
added index_sequence_that helper trait
added is_not_primitive (needed by mapply)
only test for NA from primitives once globally. test for NA from things iterated over in the iterator code
fix mapply iterator copy ctor, was not copying any_prim_na correcly
NA handling in sapply
mre on NA handling