Update S3 API for consistent formatting
Add EncodingType parameter to S3.listObjects()

Allows returned object keys to be URL encoded if EncodingType
is set to 'url':

```javascript
var params = {Bucket: 'myBucket', EncodingType: 'url'};
s3.listObjects(params, function (err, data) { ... });
```

See the Amazon S3 documentation on [GET Bucket][1] for
more information.

[1]: http://docs.aws.amazon.com/AmazonS3/latest/API/RESTBucketGET.html