Add support for AWS bucket website redirects

S3 buckets can redirect all requests to another host name (useful for static website hosting).
Since I could not find support for this in Fog, I added it.

To use, add :redirect_to => REDIRECT_TARGET to options hash for
put_bucket_website, e.g.: `connection.put_bucket_website("www.example.com", nil, :redirect_to => "example.com")`

To my eternal shame I have to confess that I have no idea how to write a spec for this, and looking at the existing put_bucket_website didn't help me any.