Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
my previous reply to your previous comment should clear this up:

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 as per 1.3 (and thereby remains oblivious to this concern). If the Subscriber dispatches asynchronously, then either always to the same thread or it must synchronize.