switched to app.use()-style

I'm not saying that you should accept this PR, but I want to discuss the approach.  I'm not a fan of the `swagger(app, {...` way of tying-in swagger as its not as clear what its doing and would rather use a `app.use('/mount-here/',swagger(...` approach (similar to what https://github.com/fliptoo/swagger-express uses).  I realize that I could achieve the same thing another way, but I just wanted to see what you thought.