• MDPrivateKeys allows the specification of several key types and the module will
  obtain a certificate for each key. This allows the parallel use of RSA and ECDSA
  certificates for the same domain (requires an Apache 2.4.41 or newer).
• Beside "RSA" plus optional key lengths, elliptic curves can be configured. Let's
  Encrypt seems to support P-256 and P-384 for now.
• Tests run with multiple certificates. Certificates are listed in status reports. The
  "server-status" html table gives individual links. Expiry durations are aggregated.
  OCSP stapling picks up the new certificates nicely.
• The JSON format for reporting certificates changed, not sure if it stays now as it
  is or if there should be come backward compat with 1 cert use.
• MDPrivateKeys checks for duplicate key specifications. There can only be one RSA key
  and a curve name can also only appear once.
• Test case for curve "x25519" is being skipped as this key does not work correctly - yet.