title: Proper way to stop Akka Streams on condition
body: <p>I have been successfully using <a href="http://doc.akka.io/api/akka/2.4/?_ga=1.140568374.588201913.1464855311#akka.stream.scaladsl.FileIO$" rel="noreferrer">FileIO</a> to stream the contents of a file, compute some transformations for each line and aggregate/reduce the results. </p>
  
  <p>Now I have a pretty specific use case, where I would like to stop the stream when a condition is reached, so that it is not necessary to read the whole file but the process finishes as soon as possible. What is the recommended way to achieve this?</p>