async/await

[nwoeanhinnogaehr]

Using Future combinators can be quite unwieldy (see audio io for example) so writing modules is currently awkward. Data must be moved between processing stages explicitly in the current model. Async/await should improve this.

Ideally I think the module could be polled repeatedly until it is closed, in contrast to how the module is currently polled infinitely by the executor until it decides to stop itself. Maybe some kind of custom executor could handle that.