Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
I agree with @benjchristensen - that statement is a little confusing and it's already stated that the `Processor` must respect the contract of both `Publisher` and `Subscriber`.

I also mentioned in another comment that because it has to respect both contracts, unless I'm misunderstanding something here, a `Processor` is a hot `Publisher`, so in practice it can't just pipe the `request(n)` calls upstream, because it will have multiple subscribers to deal with and thus it will need to do its own buffering.