Added support for website configuration on S3 buckets

Allows a bucket on S3 to be set up as a website endpoint, as described in this document: http://docs.amazonwebservices.com/AmazonS3/latest/dev/WebsiteHosting.html. Supports custom index and error documents for a bucket.

Briefly, the code's API works as a follows.

```ruby
bucket.website = {
  :index_document => 'default.html',
  :error_document => 'error.html'
}

bucket.website.index_document #=> "default.html"

bucket.website.delete
```

Please find the specs to test this functionality added to the spec directory.