title: Boost logging in 2 files with rotation
body: <p>I am using Boost for storing logs in files. Everything is fine, the rotation works, but is there a possibility to rotate the logs in just two files? I would like to have just two files of maximum 250 MB size and if one is filled, then it stores the logs in the other file ad if the second is filled, then the first one is going to be cleaned and the new logs are going to be stored there... and so on. Is it possible via Boost?</p>
  
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  <p>I have see that there is a <code>sink-&gt;locked_backend()-&gt;set_close_handler(&amp;foo);</code>, isn't there a possibility to use that function to delete the old log file? (Until now I have not managed to find it)</p>