Responses as array instead of `\Stdclass`

[atymic]

Currently all of the responses are objects, but i'd prefer them as arrays. Could we make this configurable?

Would be happy to PR.

[robertsonwang]

Please go ahead and submit a PR. Thank you!

[atymic]

PR open in #4
Also #3 to fix the tests (#4 is branched from #3)