Collection isn't iterable

Howdy, y'all 👋,

I wanted to use a `for .. of`-loop on a `Collection` and noticed that it isn't an iterable.

The fix would be rather simple; the class needs to implement `Symbol.iterator`, like so:

```javascript
class Collection {
  *[Symbol.iterator]() {
    yield* this.__paths
  }
}
```

I am happy to provide a patch with tests 💯 

Thanks!
Johannes