(MAINT) Update docs to include :unbuffered-stream
(MAINT) Update docs to include :unbuffered-stream

I also added a caveat to the usage of the :stream response body so
users know the behavior isn't streaming, just returns an instance of
InputStream.

camlow325/clj-http-client,puppetlabs/clj-http-client,rlinehan/clj-http-client,puppetlabs/clj-http-client,rlinehan/clj-http-client,camlow325/clj-http-client