Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
It is not ambiguous, there is an “or” in the sentence: only if not all calls happen from the same thread, then the Subscriber needs to ensure synchronization. If the Subscriber happens to borrow the Publisher’s thread then it effectively makes use of the Publisher’s synchronization (and thereby remains oblivious to this concern). If the Subscriber dispatches asynchronously, then either always to the same thread or it must synchronize. Sounds like a fair deal to me.