Make ServeMux public.

Sometimes, there is a need to create and use not default ServeMux. It is possible to do like this: 
serveMux := http.NewServeMux()
serveMux.HandleFunc("/", someHandler)
...
err := http.ListenAndServeTLS(":10443", "cert.pem", "key.pem", serveMux)
...

It is useful, when you need to serve different APIs on different ports within one server.

However, it is not possible while using go-restful, because Container serveMux parameter is private.
To my mind, it is logical to make it public to be able to use functionality mentioned above. Moreover, it is public in net/http library.