These public interfaces and factory classes `BufferOpening`, `BufferClosing`, `BufferOpenings`, `BufferClosings` will need to go somewhere else because `rx.operators` is not part of the public API exposed in Javadocs: http://netflix.github.io/RxJava/javadoc/

Everything inside `rx.operators` is considered an implementation detail: https://github.com/Netflix/RxJava/blob/master/rxjava-core/src/main/java/rx/operators/README.txt

So, where does it make sense for these to live?

- `rx.util`
- inner classes of `Observable`
- inner classes of `rx.util.Buffers` utility class
- somewhere else?