feat: Allow nonrecursive whole-function dependencies (#2)

And implement negate on numbers, and use dependencies to define subtract.

Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Reviewed-on: #2

generic/subtract.mjs

@@ -0,0 +1,3 @@
+export const subtract = {
+   'any,any': [['add', 'negate'], ref => (x,y) => ref.add(x, ref.negate(y))]
+}