Added doOnSubscribe() to Observable
Decouple Dispose Function for Using

As per discussion at https://github.com/Netflix/RxJava/issues/1466
Merge pull request #1589 from g9yuayon/operatorOnUnsubscribed

Added doOnSubscribe() to Observable
and... the inevitable javadoc enhancements (for the new doOnUnsubscribe method)...
doOnSubscribe
Merge pull request #1593 from benjchristensen/doOnSubscribe

doOnSubscribe
reactive.io: RxScala getting started examples
RxScala: Add mapping to RxJava doOnUnsubscribe
javadoc enhancements for the new doOnSubscribe() method
reuse existing methods
RxScala: Add mapping to RxJava doOnSubscribe

- Fix doOnUnsubscribe JavaDoc to not use @code/@link
RxScala: JavaDoc fixes to not use code or link
RxScala: Change "multicast" to be consistent with RxJava
Make retryWhen the same with the Scheduler as the retryWhen without the Scheduler.
removed the unnecessary ` extends Notification<?>` from repeatWhen too.
Merge pull request #1602 from abersnaze/consistent-retrywhen

Make retryWhen the same with the Scheduler as the retryWhen without the Scheduler
Merge pull request #1600 from jbripley/rxscala-javadocfixes

RxScala: JavaDoc fixes to not use code or link
Merge pull request #1598 from jbripley/rxscala-doonunsubscribe

RxScala: Add mapping to RxJava doOnUnsubscribe
Merge pull request #1599 from davidmoten/reuse

reuse existing methods
Merge pull request #1597 from GeorgiKhomeriki/master

reactivex.io: RxScala getting started examples