title: Is there any destroy hook for pipes in angular2 (same as for components)?
body: <p>After investigating for several days(!?!) for a huge memory leakage of my current Angular2 application, I came up with the new discovery:</p>
  
  <p>Apparently, an async pipe, which was heavily used throughout the application, was subscribing for an observable, but was never released (unsubscribed) when component and pipes where cleaned-up.</p>
  
  <p>It accumulated to a number of ~11,000 observers for a single observable with very few user actions (which eventually caused the app to crash).</p>
  
  <p>I need to unsubscribe the observable, and in order to do that I need a hook for destruction, similar to ngOnDestroy, but for pipes.</p>
  
  <p>Is there any such hook, or if not, how would you suggest to unsubscribe? </p>