Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
What does "provide for overflow protection" mean here? Emit an `onError`? I can understand overflow if the count was monotonically increasing but outstanding requests was less than 2^63-1 ... but what if the total outstanding requests actually hits 2^63-1? That's an error I believe. 

I suggest being more precise with this wording around overflow protection and hitting the limit.