2.x: concatWith/mergeWith Completable for Single and Maybe

[arekolek]

Similar in vein to #5350, is there place in this library for methods that would void the need for extension functions like those four?

fun <T> Single<T>.concatWith(completable: Completable): Single<T> {
    return toObservable().concatWith(completable).singleOrError()
}

fun <T> Single<T>.mergeWith(completable: Completable): Single<T> {
    return toObservable().mergeWith(completable).singleOrError()
}

fun <T> Maybe<T>.concatWith(completable: Completable): Maybe<T> {
    return toObservable().concatWith(completable).singleElement()
}

fun <T> Maybe<T>.mergeWith(completable: Completable): Maybe<T> {
    return toObservable().mergeWith(completable).singleElement()
}

[akarnokd]

With Kotlin, you can have all sorts of extension methods yourself, there is no need to have them in RxJava itself. I don't think these paeticular convenience methods are worth it. You may try RxKotlin though.