RxKotlin 2.0 Official Release

This is the official release of RxKotlin 2.0, backed by RxJava 2.0.7.

The notes from the RxKotlin 1.0 release apply, but there are a few additional things to call out in this release:

• RxKotlin 2.0 supports RxJava 2.x (RxKotlin 1.0 supports RxJava 1.x)
• Observable, Flowable, Single, Maybe, and Completable types are targeted with extension functions
• subscribeBy() supports both Observers and Subscribers
• Disposables and Subscriptions are both supported with convenience extension functions
• Non-null enforcement is applied to extension function factories targeting Kotlin types, since RxJava2 does not support null emissions
• A small set of operators targeting Observable<Single>, Flowable<Single>, Observable<Maybe>, etc are implemented as extension functions.
• Maven groupId has been changed to io.reactivex.rxjava2
• Root package is now io.reactivex.rxkotlin

Special thanks to @stepango for doing a lot of the work porting this over to RxJava2.