Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
How is a publisher in a "completed" state? A `Subscription` may be (it has already emitted a terminal event) and a `Subscriber` definitely can be, but a `Publisher` doesn't have such a state. 

I suggest removing this point and just leaving 1.14 to cover this as a `Publisher` can `onError` if it wants to, but that has nothing to do with being in a "completed" state.