Ability to exit entire router

[blakeembrey]

From expressjs/express#2241, add the ability to skip the rest of the router. I could have sworn I commented on the issue, but I can't find it anyway.

Use case: Automatically setting up validation middleware (from RAML). I don't want two conflicting routes to run, so exiting on the first handled would be preferable to potentially buggy and confusing behaviour.

[dougwilson]

Also additional discussion in expressjs/express#2371