feat: Initial core of picomath

Implements a totally simplistic "poortf" mutable typed function and
  a picomath instance generator, as well as the very beginnings of a
  number type and one generic function and a default full picomath instance.

  Also provides some tests which serve as usage examples.

number/add.js

@@ -0,0 +1,6 @@
+import { allNumbers } from './number.js'
+
+export default function create(pmath) {
+    return pmath('add', [allNumbers,
+       (...addends) => addends.reduce((x,y) => x+y, 0)])
+}

number/all.js

@@ -0,0 +1,12 @@
+import createNumber from './number.js'
+import createAdd from './add.js'
+import createNegate from './negate.js'
+import createSubtract from '../generic/subtract.js'
+
+export default function create(pmath) {
+   createNumber(pmath)
+   createAdd(pmath)
+   createNegate(pmath)
+   createSubtract(pmath)
+   // not sure if there's anything reasonable to return here
+}

number/negate.js

@@ -0,0 +1,7 @@
+import { oneNumber } from './number.js'
+
+export default function create(pmath) {
+    return pmath('negate', [oneNumber, n => -n])
+}
+
+                 

number/number.js

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