Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
This boils down to the lifecycle model that we imply and where at least Ben and myself have vastly different assumptions ;-) I agree with Ben that this rule is too restrictive in that it prescribes a model that not always applies (for example an empty Publisher that always just replies with `onComplete`). What we can do is to turn this around to explain where the shut-down state mentioned in 1.17 is coming from:

    While the `Subscription` is not canceled, invoking `Subscription.cancel` MAY cause the `Publisher` to transition into the shut-down state if no other `Subscription` exists at this point.

The use of keepalive Subscribers then can be deduced and does not require explicit mention.