Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
This rule is about resource cleanup in case of failure: we need the ability to tear down a stream processing graph when it cannot continue, which is the reason for the “MUST propagate immediately” part. And we also want to support the notion of bulkheads (i.e. recovery stages) that limit how far the tear-down spreads and which then can re-establish the stream or fall back to different sources, etc. This is the only rule beyond 4.1 that is actually necessary to define sane semantics of processing networks.