document new DelayError variants of various operators

[DavidMGross]

see:

• 1.x: switchOnNextDelayError and switchMapDelayError RxJava#3765 (switchOnNext, switchMap)
• 1.x: combineLatestDelayError RxJava#3763 (combineLatest)
• 1.x: concatMap full rewrite + delayError + performance RxJava#3759 (concat)

[DavidMGross]

See also ReactiveX/RxJava#684 for context