title: Reactive Throttle returning all items added within the TimeSpan
body: <p>Given an <code>IObservable&lt;T&gt;</code> is there a way to use <code>Throttle</code> behaviour (reset a timer when an item is added, but have it return a collection of all the items added within that time?</p>
  
  <p><code>Buffer</code> provides a similar functionality it that it chunks the data up into <code>IList&lt;T&gt;</code> on every time span or count. But I need that time to reset each time an item is added.</p>
  
  <p>I've seen a similar question here, <a href="https://stackoverflow.com/questions/7597773/does-reactive-extensions-support-rolling-buffers">Does reactive extensions support rolling buffers?</a>, but the answers don't seem ideal and it's a little old so I wondered if the release version of Rx-Main now supports this functionality out the box.</p>