Whitespace.
Making `Client(api_key_file)` a valid auth identifier.

Previously it was called `Client(api_key_file_location)` -- this makes things
match our naming conventions with the other SDKs.

For backwards compatibility, api_key_file_location is still respected.
Updating mock tests for `Client(api_key_file)`.
Making `Client(api_key_id, api_key_secret)` valid.

This is in favor of `Client(id, secret)` -- and normalizes our naming
conventions.
Making our client load from environment variables automatically.
Updating changes.
Adding tests for environmental auth.