feat: Add complex numbers

With just the operations we have for numbers, and overall tests.

number/number.js

@@ -1,14 +1,18 @@
+export function isNumber(x) {
+   return typeof x === 'number'
+}
+
 export function allNumbers(args) {
-    for (let i = 0; i < args.length; ++i) {
-        if (typeof args[i] !== 'number') return false
-    }
-    return true
+   for (let i = 0; i < args.length; ++i) {
+      if (!isNumber(args[i])) return false
+   }
+   return true
 }
 
 export function oneNumber(args) {
-    return args.length === 1 && typeof args[0] === 'number'
+   return args.length === 1 && isNumber(args[0])
 }
 
 export default function create(pmath) {
-    return pmath('number', [() => true, x => Number(x)])
+   return pmath('number', [() => true, x => Number(x)])
 }