Allow to use slashes in the API declaration

According to Swagger v1.2 spec, API docs consist of Resource Listing and API Declaration. In some cases it's handy to have Resources prefixed. However, current version of fnhouse-swagger can't do this, because fnhouse's router will pass `api` for `:uri-args` if resource path is `/api/foobar` and this will result in 404. This PR fixes the issue using :** variable.

The other way around would be to allow custom `context` in `ring.swagger.core/basepath`, but it's a separate issue.