2.0.0-RC4 release preparations

[akarnokd]

Version 2.0.0-RC4 - October 7, 2016 (Maven)

This release contains new operators, further cleanups, better test coverage and bugfixes. Thanks to the respective contributors and @JakeWharton for the reviews.

API enhancements

• Pull 4589: Add singleOrError, firstOrError, lastOrError & elementAtOrError to Observable and Flowable
• Pull 4616: Add Completable.andThen(MaybeSource)
• Pull 4614: Add Maybe.flatMapSingle
• Pull 4617: Add Single.flatMapMaybe
• Pull 4585: Evaluate Schedulers initialization via Callable
• Pull 4607: TestSubscriber & TestObserver add assertValue(Predicate).
• Pull 4627: Use predicates in BaseTestConsumer.assertError(Class/Throwable) to remove duplicate code, tests tweaks to remove few IDE warnings
• Pull 4629: Add Completable.fromRunnable()
• Pull 4631: TestConsumer don't wrap with CompositeException when there is only one error
• Pull 4604: add flattenAs{Observable,Flowable} to Single and Maybe
• Pull 4658: Observable.compose to use ObservableTransformer.
• Pull 4667: Add flatMap{Completable, Maybe, Single} operators to Flowable and Observable.
• Pull 4672: Remove Function from transformer interfaces to allow a single obj.
• Maybe.ignoreElement to return Completable.

Performance enhancements

• Pull 4612: Improve performance of Observable.flatMapIterable
• Pull 4622: Enable operator fusion in onBackpressureBuffer

Bugfixes

• Pull 4590: Report errors from onError to Plugin when done.
• Pull 4592: UnicastSubject fix onTerminate
• Pull 4593: Enhance NPE messages
• Pull 4603: RxJavaPlugins - Don't pass null throwable down to Error Handler
• Pull 4619: Make CompositeExcepetion thread-safe like 1.x and also fix some issues.
• Pull 4645: Signal NPE ObservableAmb FlowableAmb
• Pull 4651: Switch Maybe and Single to use their Transformers in compose().
• Pull 4654: Upcast ConcurrentHashMap to Map to avoid compatibility issue.

Removals

• Pull 4595: Remove takeFirst(predicate) from Observable & Flowable

Other

• Pull 4647: Merge AmbArray and AmbIterable into Amb for Single, Maybe and Completable types.

[akarnokd]

Closing via RC4