Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
Agreed. We should also differentiate between the Publisher being called (`subscribe`, `cancel`, `request`) in which case this rule applies, and the Publisher calling the Subscriber which should not be regulated because it does not affect the interplay of the Reactive Streams components (the only aspect to regulate in this case is what the Subscriber is supposed to do or not do).