Ianoc/case class tuple converters

Tests won't pass as relies on macro code in an as yet un-released version of bijection
What is the use case here? For Pig, the data people write is generally (always?) just primitive + strings right? Also, for DB it is the same thing. So, I would tend to say it would be good to error in this case.

We could take a boolean to `onlySimpleTypes: Boolean` or something.