Allow to generate Request object based on documented examples

[shulard]

It’s possible to add examples inside the OpenAPI documentation. Since Raven is able to generate requests to be validated I think that it’ll be awesome to retrieve documented examples and build requests with the values…

Today, raven isn’t able to parse the OpenAPI documentation by itself. It also doesn’t provide any interface to be implemented about the parsing logic. We might consider being compatible with the well known parsers ?