Looking for contributors to upgrade this project to HTTP v1

[rolinger]

If anyone wants to migrate/upgrade this API please have at it. It is light and nimble but is going to require a decent amount of rewrites to support the HTTP v1 API - the Legacy FCM api that this repository interfaces with is now retired and not supported anymore.

For the moment, I am moving to "firebase-php" as it is an active and fully supported HTTP v1 interface. I don't need all the extra stuff from firebase-php, yet I also do not have the time to recode this php-fcm repo.