Fix ObserveOn and add ParallelMerge Scheduler overload

- ObserveOn was not correctly recursing when the source was async. It would create a new scheduler (i.e. a new thread) each time.
- Also added unit tests to ParallelMerge
Merge pull request #502 from benjchristensen/observeOn-parallelMerge

Fix ObserveOn and add ParallelMerge Scheduler overload
Scala Bindings Refactor
Reorg Scala Structure

- make Eclipse and Java/Scala interop happy
Updated README
Merge pull request #503 from Applied-Duality/scala-bindings

New Scala Bindings
0.15.0-SNAPSHOT
[Gradle Release Plugin] - pre tag commit:  '0.15.0'.
[Gradle Release Plugin] - new version commit:  '0.15.1-SNAPSHOT'.
Version 0.15.0