title: usage of BulkIndexRequest from golang package 'elastic'
body: <p>I want to use <code>BulkIndexRequest</code> from Go package <code>elastic</code>. I try to find examples but it seems that they don't exist. So if anybody has used it, could you please help me to use it for creating request something like below?</p>
  
  <pre><code>curl -s -H "Content-Type: application/json" -XPOST localhost:9200/someindex/sometype/_bulk -d'
  { "index": {"_id": "existing_id"}}
  { "field1": "test1"}
  { "index": {"_id": "existing_id2"}}
  { "field2": "test2"}
  '
  </code></pre>