title: How to use placeholder with intl.formatMessage
body: <p>I'm trying to use <code>react-intl</code> to add localization to my app. Like this</p>
  
  <pre><code>&lt;FormattedHTMLMessage id="marker.title" values={{
          name: (b.name !== null ? b.name : "Bench"),
          seats: Tools.showValue(b.seats),
          material: Tools.showValue(b.material),
          color: Tools.getColorNameFromInt(b.color),
          lat: b.lat,
          lng: b.lng,
      }}/&gt;
  </code></pre>
  
  <p>But I need a string so I tried this</p>
  
  <pre><code>const title = this.props.intl.formatMessage({
      id: "marker.title",
      values: {
          name: (b.name !== null ? b.name : "Bench"),
          seats: Tools.showValue(b.seats),
          material: Tools.showValue(b.material),
          color: Tools.getColorNameFromInt(b.color),
          lat: b.lat,
          lng: b.lng,
      }
  });
  </code></pre>
  
  <p>and I get the following error message:</p>
  
  <pre><code>Error: The intl string context variable 'name' was not provided to the string '{name}&lt;br/&gt;Seats: {seats}&lt;br/&gt;Material: {material}&lt;br/&gt;Color: {color}&lt;br/&gt;Location: {lat} / {lng}'
  </code></pre>
  
  <p><code>en.json</code></p>
  
  <pre><code>{
    "marker.title": "{name}&lt;br/&gt;Seats: {seats}&lt;br/&gt;Material: {material}&lt;br/&gt;Color: {color}&lt;br/&gt;Location: {lat} / {lng}"
  }
  </code></pre>