Implement bulk style API

[dadoonet]

As we have in Elasticsearch, that'd be great to have a Bulk API which would automatically index documents with at most 100 documents per request. So instead of managing this on the client level, devs would only write things similar to:

BulkProcessor bulkProcessor = BulkProcessor.builder(
         new SimpleLoggerListener())
        .setBulkActions(bulkSize)
        .setFlushInterval(TimeValue.timeValueSeconds(5))
        .build();

Then using it is only writing things like:

for (int i = 0; i < 100000; i++) {
  bulkProcessor.add(json);
}