2.0.2 release preparations

[akarnokd]

Version 2.0.2 - December 2, 2016 (Maven)

API enhancements

• Pull 4858: add Maybe.flatMapSingleElement returning Maybe
• Pull 4881: Add @CheckReturnValue annotation to aid static verification tools

Performance enhancements

• Pull 4885: Dedicated reduce() op implementations

Bugfixes

• Pull 4873: TestObserver shouldn't clear the upstream disposable on terminated
• Pull 4877: Apply missing RxJavaPlugins.onAssembly on ops
• Commit bf0c: Fix firstOrError converted back to Observable/Flowable not reporting NoSuchElementException.