Change ToString to use original rather than foldedCase

[bergmark]

Is there a reason behind using foldedCase? It's unintuitive to me as e.g. toString . mk isn't the identity.

If we change this I think it calls for a major bump.

[hesselink]

You added it ;) I think you're right, it's probably better to use original. As for laws, fromString . toString = id makes sense to me, but that one holds in either case. I think toString . fromString = id is too string, that removed any opportunity for normalization without storing the original string. So in the end I think this choice is just one of preference.