Future based handles

This adds support for sync and async (Future-based) handlers and processors.
That's the last piece I needed to connect the whole thing to my DB and HTTP-based authentication processor ;)

The chaining is still not perfect, I don't like the forced Future.sync() which clutters the whole thing. But unfortunately I think it's necessary for now to provide support for both sync and async methods. Also now there should be no exceptions leaking which could crash the server.

The unit tests also get quite cluttered, and I had to adjust the duration of the shutdown timers multiple time. Not the nicest solution. If this grows bigger the tests need some cleanup ;)

Have a look at it and tell me what you think.