feat: Add complex numbers

No negation (and therefore no subtraction) since that needs self-reference.

test/custom.mjs

@@ -0,0 +1,21 @@
+import assert from 'assert'
+import typed from 'typed-function'
+import PocomathInstance from '../PocomathInstance.mjs'
+import * as numbers from '../number/all.mjs'
+import * as complex from '../complex/all.mjs'
+
+const bw = new PocomathInstance('backwards')
+describe('A custom instance', () => {
+   it("works when partially assembled", () => {
+      bw.install(complex)
+      assert.deepStrictEqual(bw.add(2, bw.complex(0, 3)), {re: 2, im: 3})
+   })
+
+   it("can be assembled in any order", () => {
+      bw.install(numbers)
+      typed.addConversion({from: 'string', to: 'number', convert: x => +x})
+      assert.strictEqual(bw.subtract(16, bw.add(3,4,2)), 7)
+      assert.strictEqual(bw.negate('8'), -8)
+      assert.deepStrictEqual(bw.add(bw.complex(1,3), 1), {re: 2, im: 3})
+   })
+})