Code review comment for lp:~leonardr/launchpadlib/anonymous-access

This branch introduces a new _AccessToken subclass, AnonymousAccessToken. You can use it to get read-only public access to the Launchpad web service, without authenticating as any particular user.

I also added a login_anonymously() convenience method to Launchpad. Because anonymous access doesn't go through the normal credential-obtaining process, I couldn't have this method defer to login(). I refactored some login() code into _get_paths() so that it could be used by both login() and login_anonymously().

Anonymous credentials are not stored on disk.