Add the ability to specify an API version

This is related to https://github.com/wordnik/swagger-core/issues/712.

I have also created some documentation: https://github.com/wordnik/swagger-core/wiki/API-Filtering

This feature allows me to maintain several versions of an API in the same code base. The path name is then used as a filter ("v1", "v2", etc.). The default API can then be used to point to one of the APIs as well as configure in the routes file.

This has only been developed in Scala Play. It should work in Java, but has not been tested there.