Support Google "OAuth 2.0 for TV and Limited-Input Device Applications"

[markandrus]

With some minor changes, this library can be made to work with Google's "OAuth 2.0 for TV and Limited-Input Device Applications". There are just two small changes to make:

• Google returns a verification_url instead of verification_uri, and
• Google requires the client_secret when polling for tokens.

Example authentication

Copy code: QCP-GZV-LGZ
then open: https://www.google.com/device
Access token: $ACCESS_TOKEN

[markandrus]

Thanks, @mislav! I overlooked that I broke compatibility for PollToken, thanks for fixing it 🙌 — and I can get rid of my private fork now, woohoo 🕺