• h2 + h2-16 will be negiotiated/upgraded. Priority handling is implemented
  in nghttp2, however assigning requests to workers has currently not the
  necessary information.
• Alt-Svc support based on https://http2.github.io/http2-spec/alt-svc.html
  Configuration directives H2AltSvc and H2AltSvcMaxAge added. Configurable
  per virtual host.
• reduced lock contention and eliminated broadcast signalling on internal
  condition variables, improved multi-thread performance