Numfmt v3.0

Dramatic overhaul of the parser and interface inspired by #42, the need to expose types (#38), and locale issues (#23).

### Changes from 2.0:

- Formatters are no longer constructed. Formatting is just a simple call. 
   Fixes: #42

- Types are now exposed for the entire interface.
  Closes #38

- _nbsp_ option is now off by default. A non-breaking space is till used as the grouping separator in the default locale, so "13 203" should not linebreak.

- `formatColor()` now returns `null` if pattern does not define a color. Previously it would default to "black".
   Fixes #40

- _locale_ has been fixed so that a pattern may correctly override a locale. The expected behaviour is to be able to provide a default locale and that formatters override it by modifiers.

- Both _en_US_ and _en-US_ styles are now supported for locale tags.

- Group sizing is now controlled by an option, `{ grouping: [ 3, 3 ] }`
  The formatter had remnants of behaviour from [its ancestor](https://github.com/borgar/ldml-number) which allowed defining group sizing in the format. In Excel, `#,##,##0` and `#,##0` are equivalent but sizing is controlled via locale settings.
  Fixes #48

- `dateToSerial()` no longer passes non-dates through. If it gets incompatible input (such as a number), a `null` will be returned.

- _nativeDate_ option has been removed. This affects two things:
  - `dateFromSerial()` now always returns a date parts array (`[ y, m, d, ... ]`).
  - `parseValue()`/`parseDate()` can no longer return dates.

  If you need the old behaviour then here is a utility function that safely converts the output to a `Date`. 

  ```js
  function toNativeDate (dateArrray) {
    const [ y, m, d, hh, mm, ss ] = dateArrray;
    const dt = new Date(0);
    dt.setUTCFullYear(y, m - 1, d);
    dt.setUTCHours(hh, mm, ss);
    return dt;
  }
  ```

.eslintrc

@@ -1,20 +1,23 @@
 {
-  extends: [ '@borgar/eslint-config' ],
-  parserOptions: {
-    ecmaVersion: 2020,
-    sourceType: 'module',
+  "extends": [ "@borgar/eslint-config", "@borgar/eslint-config/jsdoc" ],
+  "parserOptions": {
+    "ecmaVersion": 2021,
+    "sourceType": "module",
+    "requireConfigFile": false,
   },
-  rules: {
-    'import/export': 'error',
-    'import/no-unresolved': 'error'
+  "rules": {
+    "import/export": "error",
+    "import/no-unresolved": "error",
+    "no-mixed-operators": "off",
+    "jsdoc/no-undefined-types": "off",
   },
-  globals: {
-    console,
-    Set,
-    require,
-    module
+  "globals": {
+    "console": true,
+    "Set": true,
+    "require": true,
+    "module": true,
   },
-  plugins: [
-    'import'
+  "plugins": [
+    "import"
   ]
 }