Structure

This PR would fix #77.

It includes the changes I suggested there:
- [x] Rename `samples/` to `fixtures/` it'll be clearer that it's for unit testing.
- [x] Change the `examples/` structure to match `samples/`:
  - It should be `examples/v2.0/json/**/*.json` and `examples/v2.0/yaml/**/*.yaml`

In addition, I merged together the "mads" and "wordnik" folders. It confuses me having samples grouped by the original author of the sample (because I promote [collective code ownership](http://martinfowler.com/bliki/CodeOwnership.html))

I don't want to have both mads and maxlinc "petstore-simple.json". If they serve the same purpose I'll send a PR for the existing sample. Otherwise I'll find a more meaningful name.

It might make sense to group samples by the **owner of the API** rather than the creator of the sample. In that case I think they all belong under "petstore/" or "wordnik/" and we should try to add examples for other APIs.