Make it so that `Response` contents can be lazily deserialized where necessary.

[JonathanGiles]

[vcolin7]

We could use RequestOptions to allow for passing some parameter to eagerly buffer a response's body, eagerly deserialize it, or even discard it. This parameter can be an enum, for example.

[vcolin7]

We need to think of the default behavior. Probably eagerly buffer to avoid holding onto a connection for long.