Update Scala and sbt versions
Minor clean-ups
Simplify a generated CaseDef tree in resume method

OLD:

    case (throwable @ _) if NonFatal.apply(throwable) => {
      {
        stateMachine$1.this.result.complete(Failure.apply[Nothing](throwable));
        ()
      };
      ()
    }

NEW:

    case (throwable @ _) if NonFatal.apply(throwable) => {
      stateMachine$1.this.result.complete(Failure.apply[Nothing](throwable));
      ()
    }
More complete doc comments
Merge pull request #34 from phaller/topic/docs-cleanups

Various clean-ups and docs