Add a swagger hook to filter routes

[dschenkelman]

Pretty useful if you want to hide some things that are available but don't want documented yet. Also having a function allows you to decide if you want it displayed in a local env but not prod.

Would require changing: https://github.com/mac-/ratify/blob/master/lib/SwaggerManager.js#L313 with a filter before the forEach.

I see it's already here: https://github.com/mac-/ratify/blob/master/lib/SwaggerManager.js#L13-L18 but does not allow runtime checks.