Add a way to flatten a stream of arrays of events into a stream of events

[werner291]

Hello!

Currently, I have this thing in my code:

flattenArrayStream :: forall a. Stream (Array a) -> Now (Stream a)
flattenArrayStream input = do
  ss <- liftEffect sinkStream'
  liftEffect $ subscribe (foldMap (\x -> pushSink x ss.sink)) input
  pure ss.stream

Perhaps a new combinator that does something like this the "proper" way (perhaps without using Effect?) would be useful?