Add option for :nth-child instead of :eq inside generateRecursive() method

[JaredThomas]

Thanks so much for creating a great utility plugin that is great for an interactive website editor I work with. We take the output selector and use it elsewhere, and sometimes on sites without jQuery. The generateRecursive method uses :eq() and the correct zero-based index system, but this selector fails outside of jQuery. It would be great to accept an option for :nth-child() and adjust the index by 1 that could be checked in generateRecursive(). When I find time in the next few weeks I'll try to test this out and submit a PR for your review.