Add Explicit isLoggedIn() function

We were asking the implementor to combine it with getUserInfo()
saying it should sometimes return null.

This makes more sense, and breaks up the functions a little bit.
Merge add-explicit-is-logged-in-function (#2) into master

Add Explicit isLoggedIn() function

We were asking the implementor to combine it with getUserInfo()
saying it should sometimes return null.

This makes more sense, and breaks up the functions a little bit.