RxJava 0.17.1

This version includes a fix needed after testing RxJava 0.17.0 and Hystrix 1.4 on production canaries.
Merge pull request #221 from benjchristensen/rx-0.17.1

RxJava 0.17.1
comment out javadoc
Update build.gradle
eliminate javadoc in build
Fix Future.cancel Unit Test behavior

related to https://github.com/Netflix/RxJava/pull/959
Merge pull request #222 from benjchristensen/unit-test-fixes

Future.cancel - Unit Test Fixes
Update build.gradle
Update build.gradle
[Gradle Release Plugin] - pre tag commit:  '1.4.0-RC1'.
[Gradle Release Plugin] - new version commit:  '1.4.0-RC2-SNAPSHOT'.
1.4.0-RC1
Update README.md
Update README.md
Update CHANGES.md
1.4.0-RC1
Missing 1.3.13 Release Notes
Added support for Request Cache and Reactive Execution
Do Not Reschedule Callbacks

- Use `Immediate` so that we don't add scheduling overhead unless needed.
- Reuse the Hystrix thread if it is there. The computation of the callback can be part of the Hystrix thread.
- No one using Hystrix+Observable should be doing anything blocking on those callbacks.
Semaphore vs Thread Isolation

- only SEMAPHORE reject if SEMAPHORE isolation is being used
- unit test to assert that THREAD and SEMAPHORE isolation reject independently of each other