Add HTTP router

This is the initial PR for discussing #3023 more easily.
For more info, see the commit message.

You can run the example and the tests.

My plan:
* Improve Javadoc of classes.
  Add https://github.com/sinetja/jauter/blob/master/README.rst to
  io.netty.handler.codec.http.routing.package-info.java.
  Add https://github.com/sinetja/netty-router/blob/master/README.rst to
  io.netty.handler.codec.http.router.package-info.java.
* Improve example.
* Improve based on further discussions and feedback.
I agree with @normanmaurer since:
- It is allowed for a server to answer quickly before the end of the request (according to RFC)
- But most of all browser (if not all) will ignore it as long as they don't finish the request sending...
So sadly it might be better to consume all HttpContent until Last one...
If needed, we might have a property for the handler that if true will behave by default like this (consuming everything) but if false, will behave as short answering befre end of request (if client supports it and known to support it).