Integrate Google Cloud Storage

RE: #333 

Thought I'd start with a PR right away.

I'm still making my way through the codebase. I have a test file that uses my credentials, and the pkgcloud storage API works as expected (I think).

Unfortunately, I'm still not sure how to properly integrate with the tests properly.

[This guide](https://github.com/GoogleCloudPlatform/gcloud-node/#elsewhere) shows how you can create a project & download a JSON key. That should be all you need to run the test file (+ setting the mock environment variable).

// @silvolu @erjohnso