Added doOnSubscribe() to Observable
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