Use a token based API to reduce boilerplate code.

[the-freshlord]

It might be good to explore using a token based API where tokens are used to identify and remove observers. This will remove boilerplate code like this:

dog.age.bind({ (newAge) in
    print("This is the dog's new age: \(newAge)")
}, for: self)

to:

dog.age.bind {
    print("This is the dog's new age: \($0)")
}

The bind and bindAndFire methods would return a discardable token that would be used for identifying the observer.