title: Asynchronous Task.WhenAll with timeout
body: <p>Is there a way in the new async dotnet 4.5 library to set a timeout on the <a href="https://docs.microsoft.com/en-us/dotnet/api/system.threading.tasks.task.whenall" rel="nofollow noreferrer"><code>Task.WhenAll</code></a> method? I want to fetch several sources, and stop after say 5 seconds, and skip the sources that weren't finished.</p>