• Using OCSP stapling information to trigger certificate renewals. Proposed
  by Fraser Tweedale.
• Added directive MDCheckInterval to control how often the server checks
  for detected revocations. Added proposals for configurations in the
  README.md chapter "Revocations".
• OCSP stapling: accept OCSP responses without a nextUpdate entry which is
  allowed in RFC 6960. Treat those as having an update interval of 12 hours.
  Added by @frasertweedale.
• Adapt OpenSSL usage to changes in their API. By Yann Ylavic.