3.x: update javadoc for observeOn to mention its eagerness

[akarnokd]

Flowable.observeOn and Observable.observeOn try to do as much event delivery as they can.
Add a section explaining this property to all these multi-valued observeOn overloads:

"This operator keeps emitting as many signals as it can on the given Scheduler's Worker thread, which may result in a longer than expected occupation of this thread. In other terms, it does not allow per-signal fairness in case the worker runs on a shared underlying thread. If such fairness and signal/work interleaving is preferred, use the delay operator with zero time instead."

Also link to the @see #delay(long,TimeUnit,Scheduler).

[JosemyDuarte]

Hi! Do we only need to add the quoted message in both classes? I can do it if it is ok.

[akarnokd]

I can do it if it is ok.

Sure.

Do we only need to add the quoted message in both classes?

Single, Maybe and Completable can signal only one event and thus can't exhibit the property described.

[JosemyDuarte]

Hi @akarnokd! Just one silly question:

When you say

Add a section explaining this property to all these multi-valued observeOn overloads

You mean all but observeOn(Scheduler scheduler), right?

In any case, I just created a PR with what I understood was required. Please, if there is something wrong let me know to fix it.

Thanks

[ArtyomBasharkevich]

@akarnokd could you take a look at this?
dariuszseweryn/RxAndroidBle#628
You can just test my last example, your suggestion to use delay() did not help me solve the problem.