Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
I think it's better to call this one out explicitly as it is important for people to have clarity on how the edge cases of error handling should be handled. In other words, I see it as proactively avoiding the FAQ about what "the right thing to do" is for this case. 

A note would be fine, but since we already have 1.13, it feels natural in reading order to have the very next one explains what to do if `onError` fails, thus I'd suggest putting it as a rule ... it just happens to be a rule that you achieve naturally as long as you don't do anything actively wrong (swallowing errors for example).