Merge with upstream for issue monifu/monifu#10

Observable implements timer, amb, defaultIfEmpty, dropWhileWithIndex.

Conflicts:
	monifu-rx/src/main/scala/monifu/reactive/Observable.scala
	monifu-rx/src/main/scala/monifu/reactive/Subject.scala
	monifu-rx/src/test/scala/monifu/reactive/BehaviorSubjectTest.scala
	monifu-rx/src/test/scala/monifu/reactive/BufferedObserverTest.scala
	monifu-rx/src/test/scala/monifu/reactive/ConnectableObserverTest.scala
	monifu-rx/src/test/scala/monifu/reactive/MergeTest.scala
	monifu-rx/src/test/scala/monifu/reactive/ObservableOperatorsOnRangeTest.scala
	monifu-rx/src/test/scala/monifu/reactive/ObservableOperatorsOnUnitTest.scala
	monifu-rx/src/test/scala/monifu/reactive/ObservableSanityTest.scala
	monifu-rx/src/test/scala/monifu/reactive/PublishSubjectTest.scala
	monifu-rx/src/test/scala/monifu/reactive/ReplaySubjectTest.scala