More operators for Observable<Single>, Flowable<Single>, etc.

[thomasnield]

I have added a large number of extension function operators targeting Observable and Flowable types emitting Single<T>, Maybe<T>, and Completable emissions.

@JakeWharton and @stepango, please let me know what you think of these.

[stepango]

Looks ok to me.

[thomasnield]

I am debating removing some of these operators that require a conversion to an Observable to work with an Observable operator. mergeAllMaybes() is a definite since there is a flatMapMaybe(). But concatAllMaybes() might be pushing out of scope since there is no concatMapMaybe(). This also applies to Single and Completable.

/**
 * Concatenates the emissions of an Flowable<Maybe<T>>.
 */
fun <T : Any> Observable<Maybe<T>>.concatAllMaybes() = concatMap { it.toObservable() }

/**
 * Concatenates the emissions of an Flowable<Maybe<T>>.
 */
fun <T : Any> Flowable<Maybe<T>>.concatAllMaybes() = concatMap { it.toFlowable() }

/**
 * Emits the latest `Maybe<T>` emitted through an `Flowable<Maybe<T>>`.
 */
fun <T : Any> Observable<Maybe<T>>.switchLatestMaybe() = switchMap { it.toObservable() }

/**
 * Emits the latest `Maybe<T>` emitted through an `Flowable<Maybe<T>>`.
 */
fun <T : Any> Flowable<Maybe<T>>.switchLatestMaybe() = switchMap { it.toFlowable() }

[thomasnield]

Decided to rid those operators. You can easily do a toObservable() conversion within a map() before a concatAll() or switchLatest().