Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
What happens if either of these do occur (and it will happen at some point)? I suggest the `Subscriber` must `onError` itself. If it was `request` that failed it should `onError` itself and call `cancel`. If `cancel` fails all it can do is `onError` itself.

Or we could just say it "blows up" and lets the exception throw, but that risks leaving code everywhere "hung" waiting on terminal events (such as the `onError`/`onComplete` on the `Subscriber`).