The response of the authentication should contain information about the anonymous status

[schettn]

Is your feature request related to a problem? Please describe.
Currently when calling session.begin() it is not clear wether you are logged in as an anonymous user or not.
The response contains the username and it would be possible to check if the username is the same as the anonymous user, but this would definitely create a large potential for error.

Let's look at an example:
The change of the anonymous username in v0.2.0 would be a breaking change cause every user of the snek-client had to adjust there codebase on the new username.

Describe the solution you'd like
It would be a lot cooler if the response of session.begin() would contain a boolean, let's call it anonymous which tells if I got authenticated as anonymous or not.