Added instances for NonEmptyList and accompanying spec.

I had a go at adding instances that made sense for NonEmptyList. It was mostly to learn a bit more about Monocle - I still don't grok quite a bit of this library, so any suggestions/comments welcomed.
Also - as related to #121 I failed to actually get the tests to run at all due to runnning out of heap. Perhaps I was doing something silly - but it looks ok to me.