ignoreError operator

[larryonoff]

public func ignoreError<T, E>(signal: Signal<T, E>) -> Signal<T, NoError> {
    return Signal { observer in
        return signal.observe(Signal.Observer { event in
            switch event {
            case let .Next(value):
                sendNext(observer, value.value)
            case let .Error(error):
                break
            case .Completed:
                sendCompleted(observer)
            case .Interrupted:
                sendInterrupted(observer)
            }
        })
    }
}