In the HB helpers, the hash options equate exactly to the `new Intl.NumberFormat(locales, options)` constructor `options`.

In the case above it would be `{{intlNumber 123 style="currency" currency="USD"}}`.

We could support the custom `{{intl}}` specified formats like this:

```js
res.render('foo', {
    locale: 'en-US',
    i18nFormats: {
        usd: {style: 'currency', currency: 'usd'}
    }
});
```

…and in the template:

```
{{intl locales=locale formats=i18nFormats}}
    {{intlNumber 123 @intl.formats.usd}}
{{/intl}}
```