Adds Shutdown. Moved docs to interfaces.

[wiverson]

What kind of change does this PR introduce?

Adds a Shutdown option to the auth state notification. This provides a mechanism to manually terminate the background refresh thread without logging out. This allows the client to be used cleanly when running in the Unity editor.

In addition, went ahead and moved the docs to the interfaces and inherit docs on the implementation - less copy and paste FTW.

What is the current behavior?

Only user visible / API change is the addition of the Shutdown auth state. It's possible that if client code is throwing an exception on an unexpected state change they might get an exception here. This is the kind of thing that IDEs like Rider are pretty good at catching in static code analysis FWIW.

Oh, and now the docs should be visible for IDEs when working with both the interfaces and the implementation code.

[acupofjose]

@wiverson please see comments from review ^ not sure if it sent you a notification

[wiverson]

Nope, I'm not seeing any comments...? If you want to mod/tweak just go for it of course. :)

[wiverson]

FWIW this is all I see

[acupofjose]

Turns out I have to submit it before the comment shows. Who knew? 😂