Converting [SignalProducer<U>] -> SignalProducer<[U]>

signal-collect

// https://twitter.com/davedelong/status/701621040015810560: @NachoSoto is there a way to take a # of SignalProducer<U,E> and turn them in to SignalProducer<[U], E>? Like combineLatest but w/o tuples

let signals: [SignalProducer<T, E>]

let result: SignalProducer<[T], E> = 
  SignalProducer(values: signals) // create a producer that emits all signals.
    .flatten(.Merge)              // merge all values that they emit.
    .collect()                    // collect all values into an array.