0.20.0-RC6

Further fixes and enhancements bringing us close to completing 0.20.0 and almost ready for 1.0.

A more major change in this release is the deprecation of Observable.from(T). The full discussion can be seen in #1563.

• Pull 1575 combineLatest with backpressure
• Pull 1569 Compose/Transform Covariance
• Pull 1577 Fix the compose covariance
• Pull 1581 zip(Iterable) -> zipWith(Iterable)
• Pull 1582 Deprecate GroupedObservable.from
• Pull 1583 Redo/Repeat Backpressure
• Pull 1576 from(T) -> just(T)
• Pull 1545 Make Android ViewObservable.input observe TextView instead of String

Artifacts: Maven Central