Add Feature: Make possible to explicitly specify currency when localising numbers.

[bponomarenko]

Hi. Thanks for this plugin, it works really well for us. However there is one use case, which can't be implemented with vue-i18n at the moment.

Use case

We need to display a list of formatted amounts in different currencies.
Data structure may look like this:

const transactions = [
  { amount: 10123.45, currency: 'EUR' },
  { amount: 23.00, currency: 'GBP' },
  { amount: 45.40, currency: 'USD' },
];

Feature request

Make it possible to explicitly specify currency when localising numbers.

Current set of arguments for $n() function looks like this:

• {number} value: required
• {Path | Object} key: optional
• {Locale | Object} locale: optional

This makes it possible to extend the second key: Object argument by adding optional currency option, which will override default value from the numberFormats configuration.

Example of possible API

Number formats:

const numberFormats = {
  'en-US': {
    currency: {
      style: 'currency',
      currency: 'USD',
      currencyDisplay: 'code'
    }
  }
}

Template:

<ul v-for="transaction in transactions">
  <li>{{ $n(transaction.amount, { key: 'currency', currency: transaction.currency }) }}</p>
  <!-- Or use it even as a fallback options:
  <li>{{ $n(transaction.amount, { style: 'currency', 'currency': transaction.currency, currencyDisplay:
 'code' }) }}</li>
  -->
</ul>

Expected result:

<ul>
  <li>EUR 10,123.45</li>
  <li>GBP 23.00</li>
  <li>USD 45.40</li>
</ul>

[bponomarenko]

@kazupon I can create PR if you ok with proposed API.

[kazupon]

@bponomarenko I look forward to your PR. :)

[kazupon]

closed (merge with #305)