Question after reading this: when I do `<- object.foo()` what is the precedence? Does FRB lookup `object.makeFooObserver`, `object.observeFoo`, `object.foo` and use the first one it finds, or the other way around?

I would also find it clearer if after each `Clock` implementation you showed the binding in use:

```javascript
Bindings.defineBindings({
    clock: new Clock()
}, {
    "time": {"<-": "clock.time()"}
});
```

the text says that this works, but never shows it.