query.go
func (iter Enumerator) SelectMany(lister Unfolder) Enumerator {
	retval := make(chan interface{})

	go func() {
		for parent := range iter {
			for child := range lister(parent) {
				retval <- child
			}
		}
		close(retval)
	}()

	return retval
}
func (iter Enumerator) SelectMany(lister Unfolder) Enumerator {
	retval := make(chan interface{})

	go func() {
		for parent := range iter {
			for child := range lister(parent) {
				retval <- child
			}
		}
		close(retval)
	}()

	return retval
}
// SelectMany allows for flattening of data structures.