Add option for prompting for token note

In the case where the user might have to refresh their token, it's up to the ghauth library consumer to implement their own prompting for the token note (which must be unique). This adds an option (default: falsey) to prompt the user to name their token before entering credentials.

I didn't want to bring in any dependencies (specifically for async control-flow), so I implemented a somewhat hacky solution for that conditional async action.

Anyhow, if you're interested, here it is!