https://medium.com/@benlesh/learning-observable-by-building-observable-d5da57405d87
https://www.learnrxjs.io/operators/filtering/skipuntil.html
https://xgrommx.github.io/rx-book/
http://reactivex.io/rxjs/manual/overview.html
https://bsideup.gitbooks.io/rxconnect/content/
https://github.com/bsideup/rx-connect/tree/master/examples