fix: Separate typed instance for each PocomathInstance (#15)

Also starts each PocomathInstance with no types at all, and uses the new
  situation to eliminate the need for a Complex "base case".

  Resolves #14.
  Resolves #13.

Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Reviewed-on: #15

src/number/add.mjs

@@ -0,0 +1,5 @@
+export {Types} from './Types/number.mjs'
+
+export const add = {
+   '...number': [[], addends => addends.reduce((x,y) => x+y, 0)],
+}