A guide for building custom RxJS (v6) pipeable operators https://angularfirebase.com/lessons/custom-rxjs-operators-by-example/
– Nicholas Jamieson https://medium.com/@cartant
– RxJS Pipeable Ops https://github.com/ReactiveX/rxjs/blob/master/doc/pipeable-operators.md
– PRO Members Firestore JOINS: https://angularfirebase.com/lessons/firestore-joins-similar-to-sql/