Add marble diagrams for Single.repeat operators

[UMFsimke]

Here are marbles for repeat, repeat(times) and repeatWhen operator in #5788

Please let me know if I need to change anything on the diagram itself. If not, please send me URL when you upload image within the project so I can change URL for the marble in the PR.

I intentionally added two diagrams for repeatWhen as I would say its interesting case that people should be aware of.

EDIT:
Here are marbles

repeat operator:

repeat(count) operator:

repeatWhen operator:

[codecov]

Codecov Report

Merging #6081 into 2.x will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #6081      +/-   ##
============================================
- Coverage     98.25%   98.24%   -0.02%     
+ Complexity     6195     6194       -1     
============================================
  Files           667      667              
  Lines         44856    44856              
  Branches       6211     6211              
============================================
- Hits          44074    44068       -6     
- Misses          237      244       +7     
+ Partials        545      544       -1

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/io/reactivex/Single.java	100% <ø> (ø)	146 <0> (ø)	⬇️
.../operators/observable/ObservableFlatMapSingle.java	88.8% <0%> (-6.72%)	2% <0%> (ø)
...ernal/operators/flowable/FlowableFlatMapMaybe.java	90.82% <0%> (-4.35%)	2% <0%> (ø)
...nternal/operators/parallel/ParallelReduceFull.java	91.08% <0%> (-3.97%)	2% <0%> (ø)
...tivex/internal/observers/FutureSingleObserver.java	94.33% <0%> (-3.78%)	24% <0%> (-1%)
...rnal/operators/observable/ObservableSwitchMap.java	93.61% <0%> (-2.66%)	3% <0%> (ø)
...va/io/reactivex/internal/queue/SpscArrayQueue.java	97.61% <0%> (-2.39%)	22% <0%> (-1%)
...ava/io/reactivex/processors/BehaviorProcessor.java	96.86% <0%> (-2.25%)	60% <0%> (ø)
.../io/reactivex/disposables/CompositeDisposable.java	98.14% <0%> (-1.86%)	39% <0%> (-1%)
...perators/mixed/ObservableSwitchMapCompletable.java	98.94% <0%> (-1.06%)	3% <0%> (ø)
... and 24 more

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[UMFsimke]

I see few errors. Timeline for flowables should end with error/complete event and should not continue beyond them. I'll update that tomorrow

[akarnokd]

It would be great if you linked the diagrams in the PR text.

[akarnokd]

Could you also add shadows to the marbles and X?

[UMFsimke]

Updated images and PR comment

[akarnokd]

• https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.repeat.png
• https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.repeat.n.png
• https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.repeatWhen.png

[UMFsimke]

Thanks! PR is now updated