Pretty print

This ended up being more code than I would have liked.

It's the first thing I've gotten working though, so maybe we can merge it and then iterate to improve?

The big difference is that we're throwing away the Diff object that Json4s gives us and performing a text diff in the pretty print space.

It has been suggested that we could perhaps simply turn the entire request into a json string and do a single full text diff rather than matching on the error mode ADT...

Worth mentioning is that I'm not at all sure what the cases are going to look like for multiple failures... We should probably add tests for them to make sure they don't look too bad