title: Rumen and custom counters
body: <p>I am using Rumen to extract information from the job history to .json format.
  This works fine for default counters and params.
  However, I could not see the custom counters that I have added to my mappers.</p>
  
  <p>I manage to see those custom counters via the web based history interface, but they don't appear in the generated .json file by Rumen.</p>
  
  <p>Any idea on how to extract all (default + custom) counters from the job history by using Rumen ?</p>
  
  <p>Thank you.</p>