Add a reactive systems example?

[dyoder]

Since Mutual/ng provides a simple event emitter interface for Redis-based messaging, we can set up a flow to implement a synchronized counter quite trivially.

Client

In the following code ,messages is a Mutual event-emitter.

go [
  events "update", messages
  map (counter) -> data.counter = counter
]

Server

go [
  observe data.counter
  map ({counter}) -> messages.emit "update", counter
]

[dyoder]

Work has begun in examples/messaging branch.