* core: Create credentials from access token via OAuth2
* core: Credentials.username is optional: not required for token auth.
* core: store auth data within session. We might need this later if need to re-auth and original creds are no longer valid/available.
* bin: New --token arg for using Spotify access token. Specify 0 to manually enter the auth code (headless).
* bin: Added --enable-oauth / -j option. Using --password / -p option will error and exit.
* core: reconnect session if using token authentication
Token authenticated sessions cannot use keymaster. So reconnect using the reusable credentials we just obtained. Can perhaps remove this
workaround once keymaster is replaced with login5.
* examples: replace password login with token login
Re-add default impl to SessionConfig and make Credentials::with_password generic over Into<String>
add docs for Credential
reintroduce old Default impl for SessionConfig
use the third argument for the track-to-play rather than a testing id
