Tweak stats client for consistency, stub out a test

[brian-c]

Minor updates for more consistent style with the rest of the library. Mainly workflowID, not workflow_id.

Also stubbed in a dumb test just to see how it works.

[eatyourgreens]

Looks good to me.

[CKrawczyk]

@brian-c it looks like the test you added calls the stats function with params wrokflow_id and project_id instead of workflowID and projectID. As it is written the test is grabbing the events for all projects instead of for GZ bars.

[brian-c]

Thanks @CKrawczyk, just pushed up a fix.