Tweaks to NF term language and farray representation.
Simplified nfSub -> fSub function, added handling for NF_TUP_SUB nodes.
Added operator composition to NF representation, along with correct handling of NF->F ops, and better Non-Flat -> NF ops. NF now properly supports tuple projection without coalescing all tuple projections into instances of NF_ARR_SUB without array subscripts.