Initial version of spec-generated tests

~~This might not yet be ready for primetime, but here's a PR to serve as a kick-starter for discussions.~~

The spec is currently hosted on this project's gh-pages site:

* JSON: http://wikimedia.github.io/restbase/v1/swagger.json
* YAML: http://wikimedia.github.io/restbase/v1/swagger.yaml

A Swagger UI instance points to the spec, and is accessible from http://wikimedia.github.io/restbase

Tests are parsed from the `x-amples` extension fields in http://wikimedia.github.io/restbase/v1/swagger.yaml
I recommend getting the spec from the "official" documentation, wherever that ends up being (e.g. *docs.wikimedia.org/restbase/v1/swagger.yaml*).  This keeps the spec independent from the implementation, elevating it to the status of "source of truth" about the API.