VAPID
Add VAPID compatibility. Cf. WebPush 1.3 release notes.
The following config entries have been added:
VAPID:
subject: https://yoursite.com # can be an URL or a mailto:
publicKey: ~88 chars # uncompressed public key P-256 encoded in Base64-URL
privateKey: ~44 chars # the secret multiplier of the private key encoded in Base64-URL
pemFile: path/to/pem # if you have a PEM file and can link to it on your filesystem
pem: pemFileContent # if you have a PEM file and want to hardcode its content