Version 1.x can be found at https://github.com/ReactiveX/RxAndroid/blob/1.x/CHANGES.md
RxAndroid 2.0 has been rewritten from scratch to support RxJava 2.0.
The library still offers the same APIs: a scheduler and stream cancelation callback that know about
the main thread, a means of creating a scheduler from any Looper, and plugin support for the
main thread sheduler. They just reside in a new package, io.reactivex.android, and may have
slightly different names.
For more information about RxJava 2.0 see its RC1 release notes