feature: Router.Name() should create a NewRoute.

[seriousben]

Describe your problem

Most of the route's functions are exposed on the router for creating a new router. Unfortunately Name is not exposed as such.

For consistency, I believe it should be exposed.

Paste a minimal, runnable, reproduction of your issue below

r := mux.NewRouter()
// works
r.Handler("/path", httpHandler).Name("route name").Method("GET")
// works
r.Method("GET").Handler("/path2", httpHandler).Name("route2 name")
// is not supported
r.Name("route name").Method("GET").Handler("/path2", httpHandler)

[seriousben]

Working on a PR right now.