Naive schedulers implementation
New operation Finally (issue #43)
Add finally0 to Observable.java .
Missing import
Added nonstatic Observable.finally0
Incoporate review suggestions.

Splits a compound unit test into to parts.
Uses mockito instead of a bespoke test object.
Removes unused import statements.
Changes the order of the Finally action w.r.t. onComplete/onError.
Added ScheduledExecutorServiceScheduler
Added to Schedulers
More tests
Headers
ObserveOn/SubscribeOn unit tests
Some documentation
Documenting code
renamed tests
Extracted ScheduledObserver as a separate class
Synchronize Observer on OperationMerge

fixes https://github.com/Netflix/RxJava/issues/200

This is necessary because by definition Merge is subscribing to multiple sequences in parallel and is supposed to serialize them into a single Observable.
Synchronization of Merge operator (fixes)

- return AtomicSubscription not MergeSubscription which I was accidentally still returning
- try/finally in unit test so threads are released even if assertion is thrown
Add tests to demonstrate bugs
Merge branch 'upstream' into issue43
Split Take and TakeWhile