Async render interface

[sgammon]

Is there any way to invoke the async eventloop in a render() call? It seems like it is synchronous within the scope of view rendering.

Soy, for instance, supports "continuations" during render. You can pass in a Future<X> for any template context parameter X. Rendering occurs until an async value is needed, at which point, the render process bails out in a way that is "resumable," so to speak.

Before resuming this render, the simplest option is simply waiting on the Future, which is what I do now in the Soy-related PR. However, it would be extra cool to have the ability to yield to the reactor, so that it can process other things or otherwise know when the view renderer is waiting on some future value.