feat: Add all remaining features of original Picomath PoC (#5)

Namely, a README describing the proof-of-concept,
  a custom selective loader, and some additional tests.

Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Reviewed-on: #5

complex/extendToComplex.mjs

@@ -0,0 +1,19 @@
+import './Complex.mjs'
+import * as complex from './complex.mjs'
+
+/* Add all the complex implementations for functions already
+   in the instance:
+*/
+
+export default async function extendToComplex(pmath) {
+   pmath.install(complex)
+   for (const name in pmath._imps) {
+      const modulePath = `./${name}.mjs`
+      try {
+         const mod = await import(modulePath)
+         pmath.install(mod)
+      } catch (err) {
+         // Guess it wasn't a method available in complex; no worries
+      }
+   }
+}