1.x: Feature Request Single#flatMapCompletable

[vanniktech]

Would be nice to flatMap from Single to Completable unless there is any other way to do this right now. flatMapObservable already does exist.

Happy to hear thoughts on that from you guys.

[akarnokd]

PR welcome.

[vanniktech]

I'm curious how would you start implementing this?

[akarnokd]

Subscribe to the Single and in the onSuccess, call the mapper and subscribe to the returned Completable.

[akarnokd]

Closing via #4226.