title: ReactiveCocoa 4 - Delaying and filtering signal events
body: <p>I am implementing a search textfield using ReactiveCocoa 4, and want to only hit the search API after no text has been inputted for X amount of time. I have done this previously by canceling previously scheduled and firing off a "executeSearch" selector in the textDidChange delegate method. This ensures that every time I type, any previously scheduled "executeSearch" selector is canceled, and a new one is scheduled to fire in X seconds.</p>
  
  <p>I now want to do this same behavior, but from a signal producer bound to my input text.  My current implementation is close, but not the same. This behavior merely throttles the text input event to only fire every 0.5 seconds, instead of canceling the previous event.</p>
  
  <pre><code>searchTextInput.producer.delay(0.3, onScheduler: RACScheduler.currentScheduler())
                          .throttle(0.5, onScheduler: RACScheduler.currentScheduler())
                          .producer.startWithNext({ [unowned self] searchText in
                             self.executeSearch(searchText)
                          })
  </code></pre>
  
  <p>I'm having a hard time sifting through the ReactiveCocoa 4 documentation to know which signal functions I should be using! Thank you!</p>