Correlation of Reactive Streams signals to IO kernel events

[jbrisbin]

This was introduced in issue #7, but we probably need a separate issue to discuss how IO kernel events are translated into Reactive Streams signals (assuming that RS signals are the only way to communicate with abstract components).

[jbrisbin]

The range of possible signals is:

• Publisher.subscribe
• Subscriber.onSubscribe
• Subscriber.onNext
• Subscriber.onError
• Subscriber.onComplete
• Subscription.request
• Subscription.cancel

It will be important to determine which of these 3 possible abstractions each IO kernel component corresponds to (or depends on).