Adding toString to BatchedIterator.
Adding toString to ChainedIterator.
Adding toString method to ComprehensionIterator.
Adding toString to CyclicIterator.
Adding toString to EachIterator.
Adding toString to FilteredIterator.
Adding toString method to MappedIterator.
Adding toString to PredicatedIterator.
Adding toString to ZippedIterator.
Adding toString to SubSequenceIterator.
Merge pull request #167 from tobyclemson/iterator-to-string

toString methods on Iterators