v3 API login changes

In v3, the API sign in request body field names have been updated.

v2	v3
Sign in with `POST /v2/Login.json`.	Sign in with `POST /v3/login`. In the request body, the field names have been updated. The response is not in a `response_data` object. See /v3/login in the API reference for more information.
Sign out with `POST /v2/Logout.json`.	Sign out with `POST /v3/logout`. The response is simply a `200` without any response fields.

In the request body, the field names have been updated. The response is not in a response_data object.

See /v3/login in the API reference for more information.

Sign out with POST /v2/Logout.json.

Sign out with POST /v3/logout.

The response is simply a 200 without any response fields.