sessions_between_states metric

Similar to sessions_until_state metric, but allows you to specify the state where you start counting sessions.  This will allow you to evaluate specific sections of an app's performance in terms of session count.
Good question.  I'm leaning towards using 1 here, my thinking is if we use 0 I'd rather call it new_sessions_between_states.  Let's get hodgestar's opinion, though.