Prepare for 0.4.0.M1

Docs tweaking and package info renaming in README.md
@benjchristensen - I believe we are in agreement about this issue. 

But, the reason for why I consider `Processor` to be a hot `Publisher` is because, by the contract of its API, it doesn't have access to a `subscribe()` function that it can use to create new subscriptions. All it can do is to listen to whatever comes on its own `onXXX` methods and `.cancel()` upstream, should it want to do so. This means that if a `Processor` instance is exposed publicly to users, then it can receive multiple `subscribe()` calls - at that point it may choose to `.onError` (i.e. to be a unicast publisher that can be subscribed to only once), or otherwise it has no choice but to serve all subscribers with events from the same data source. As you said.

A `Processor` cannot be a cold `Publisher`, in the sense that it cannot create new data connections for each subscriber. It can be a *unicast* publisher, but only if it disallows multiple subscriptions (by terminating new subscribers with `onError`).

Btw, your `MapProcessor` in that example for instance throws an `IllegalStateException` in `onSubscription` if it doesn't have a subscriber already. This I believe should be a violation of the contract if it already isn't and it's also an unnecessary protection since demand can be signaled once it has a subscriber and you can cache `onComplete`/`onError` events that can happen before the first subscription. And its `subscribe()` is broken, because it forgets about previous subscriber references that were passed to it and it might end up sending `onNext` events to subscribers that haven't even requested it and that have a `null` subscription. For the purposes of your example (i.e. the implementation of an operator), this `MapProcessor` does its job, but it cannot be a public `Processor` implementation, exposed to users without strings attached, because it violates its contract. 

Sure, it is fixable and it can be a unicast publisher, but it cannot be a cold publisher, which was the point I tried to make.