Support integration with Swagger/OpenAPI

[dugancathal]

I'm envisioning a new matcher type meta-command from the ApiSim.configure block that generates matchers for each path defined by Swagger.

The new API might look something like:

ApiSim.configure do
  parse_swagger_config_at 'http://my-swagger.internal.com/path/to/swagger/config.json'
end

[dugancathal]

Looking over the documentation at http://swagger.io/specification/, this looks totally reasonable. Cursory glances around the interwebs make it look like this is not something that the Ruby community has kept up to date with.