• Main news is the ability to control the heuristics used to determine the
  expiry time for response objects.
  
• Reformat later parts of Changes
  
• Add a paragraph to summarize the motivation for releases since 5.815
  
• all_pod_files_ok();
  
• Fix POD markup error
  
• Calculation of current_age with missing Client-Date.
  
• The age/freshness methods now take an optional 'time' argument
  
• More correct matching of 'max-age' in freshness_lifetime method
  
• The freshness_lifetime method now support options to control its heuristics