Fns to create an org.eclipse.jetty.server.Server instance that conforms to the options map specified in the slipway README.

Derived from:
  * https://github.com/sunng87/ring-jetty9-adapter/blob/master/src/ring/adapter/jetty9.clj
  * https://github.com/ring-clojure/ring/blob/master/ring-jetty-adapter/src/ring/adapter/jetty.clj