Http: Java Routing API Preview

Here's the first batch of the high-level Java server API which already demonstrates a few concepts. Looking at the examples already explains much but I will write a summary as we go along as well.

Implementation is also already available (https://github.com/spray/akka/tree/w/15911-java-routing-dsl-implementation) for everything demonstrated here but omitted here for clarity.

/cc @sirthias 
Yes and no I guess. I was thinking  if we will go down the road of `handleWith(Handle[T1])`, `handleWith(Handle[T1, T2])`, `handleWith(Handle[T1...])` for this API, with lambdas or not, there would have be some types like that to make the `handle(T1 t1)` etc available ("in the long run")?