Observable.sample(Observable) in Scala
tweak RxScalaDemo (and Olympics example)
some RxScalaDemo tweaks
add Subscriber and Observable creation from `Subscriber[T] => Unit`
Merge branch 'master' of github.com:Netflix/RxJava into scala-additions
deprecate rx.lang.scala.Observable.create[T](Observer[T]=>Subscription)
correct link to maven search
A number of improvements to OperatorObserveFromAndroidComponent

- move the UI thread assert out of the operator and into the helpers; this way, we don't fail the observer anymore with an exception, but the caller.
- do not loop unsubscribe through the main thread anymore. This unnecessarily defers releasing the references, and might in fact be processed only after Android creates the component after a rotation change. I had to make the references volatile for this to work.
- immediately unsubscribe in case we detect the componentRef has become invalid. This solves the problem that dangling observers would continue to listen to notifications with no observer alive anymore.

refs:
https://github.com/Netflix/RxJava/issues/754
https://github.com/Netflix/RxJava/issues/899
add Observable.startWith(Observable) method and unit test to avoid breaking method chaining when want to startWith an Observable rather than just an Iterator or specific values.
add space to a comment to force ci rebuild to see if suspected non-deterministic test fails again
refactor the debug hooks before they become a breaking change.
math-module

Moving the average/sum/min/max functionality to the MathObservable similar to StringObservable.
Merge pull request #942 from benjchristensen/math-module

MathObservable
OperationRetry -> OperatorRetry

Updated to use "lift" and Subscriber.
Fixes https://github.com/Netflix/RxJava/issues/943 Observable.retry() does not unsubscribe from source
Merge pull request #944 from benjchristensen/operator-retry

OperationRetry -> OperatorRetry
Merge branch 'clean-up-hook-args' of github.com:abersnaze/RxJava into merge-940

Conflicts:
	rxjava-core/src/main/java/rx/Observable.java
Merge pull request #945 from benjchristensen/merge-940

Manual Merge 940
Merge pull request #934 from davidmoten/add-startWith

add Observable.startWith(Observable) method and unit test
Merge pull request #929 from devisnik/fix_maven_search_link

correct link to maven search
Merge pull request #923 from samuelgruetter/scala-additions

Observable creation from Subscriber[T]=>Unit for Scala