doff: improve generator interface slightly
No longer need to give units as named arguments, instead just the bare
values. The defaults get recognized as the "no filter" case.
:- %say
|= $: [now=@da eny=@uvJ bec=beak]
~
- [dude=(unit dude:gall) ship=(unit ship)]
+ [dude=_`dude:gall`%$ ship=_`@p`(bex 128)]
==
-[%helm-doff dude ship]
+=/ darg=(unit dude:gall) ?:(=(%$ dude) ~ `dude)
+=/ sarg=(unit ^ship) ?:(=((bex 128) ship) ~ `ship)
+[%helm-doff darg sarg]
