Add rx support to hystrix-clj.

Add observe, observe-later, and observer-later-on functions to
hystrix-clj corresponding to observe(), toObservable() and
toObservable(Scheduler) methods added to Hystrix respectively.
Merge pull request #170 from daveray/hystrix-clj-observe

Add rx support to hystrix-clj.
[Gradle Release Plugin] - pre tag commit:  '1.3.1'.
[Gradle Release Plugin] - new version commit:  '1.3.2-SNAPSHOT'.
Version 1.3.1
Create CONTRIBUTING.md
Fix Exception vs Throwable typo

- This was using the Object overload rather than statically typed Func1<Throwable> method. This was caught when testing RxJava 0.11.0 which restores static type safety.
Merge pull request #173 from benjchristensen/fix-exception-throwable-typo

Fix Exception vs Throwable typo
[Gradle Release Plugin] - pre tag commit:  '1.3.2'.
[Gradle Release Plugin] - new version commit:  '1.3.3-SNAPSHOT'.
Version 1.3.2
Reference to Clojure Version
Reference to hystrix-event-stream-clj
RxJava 0.11.0
[Gradle Release Plugin] - pre tag commit:  '1.3.3'.
[Gradle Release Plugin] - new version commit:  '1.3.4-SNAPSHOT'.