--------------------------------------------------------------------------- Class constructor. --------------------------------------------------------------------------- 
@class An object stream to list S3 objects.

Pipe in objects of the following form:

{
s3Client: new AWS.S3(),
bucket: 'exampleBucket',
// Optional, defaults to 1000. How many objects to return in one API
// request under the hood.
maxKeys: 1000,
// Optional. If present, only list objects with keys matching the prefix.
prefix: 'examplePrefix'
// Optional. If present, use to group keys.
delimiter: '/'
}

Pipe out standard response objects from the S3 listObjects API, with the
addition of the bucket name as well.

{
Bucket: 'exampleBucket',
Key: ...
LastModified: ...
ETag: ...
Size: ...
StorageClass: ...
Owner: {
DisplayName: ...
ID: ...
}
}

@param {Object} options Standard stream options.
function S3ListObjectStream (options) {
  options = options || {};
  // Important; make this an object stream.
  options.objectMode = true;

  S3ListObjectStream.super_.call(this, options);
}