Ability to get access to the http response code on GetObject

[robacarp]

Thank you for this shard! I'm using it on https://archive.fm/ and it's working great.

I'd like to be able to ask if a GetObject request is successful or not. HTTP::Client::Response provides both #success? and #status_code / #status. At a bare minimum, it would be sufficient to just provide an accessor for the http response itself within GetObjectOutput.

What do you think? I'll be happy to submit a PR if you think it's worthwhile to add.

[taylorfinnell]

Makes sense to me, feel free to send an MR.