migrate unit tests for Groovy to separate Groovy file

- testing all Groovy functionality doesn't belong as an inner class
- it was awkard to load Groovy scripts via Java (leftover from previous codebase where Groovy wasn't part of build, only a runtime library)
- establish convention for each language to have a suite of tests in /src/test
remove rxjava-examples

Examples have been moved into /src/examples folders of each language-adaptor subproject.
README to explain unit tests
clojure example code

- examples are in /src/examples/clojure
- placeholder for unit tests in /src/tests
groovy example code

- examples are in /src/examples/groovy
remove rxjava-examples submodule
clojure project build config
Merge pull request #132 from benjchristensen/language-tests-and-examples

Refactoring language tests and examples layout
restore performance optimization to reduce wrapping

Without optimization:

runCompositionTest
Sum: 710082754 Time: 42.353ms
runNonCompositionalTestWithDirectLoop
Sum: 710082754 Time: 17.719ms
runNonCompositionalTestWithArrayOfFunctions
Sum: 710082754 Time: 17.344ms

With optimization:

runCompositionTest
Sum: 710082754 Time: 23.064ms
runNonCompositionalTestWithDirectLoop
Sum: 710082754 Time: 18.059ms
runNonCompositionalTestWithArrayOfFunctions
Sum: 710082754 Time: 18.88ms
remove warnings and cleanup
Restoring null check removed in recent commit

See https://github.com/Netflix/RxJava/commit/caf3a9434ed4b3b4efba6661891f02417aebf604 for removal

It started causing this unit test to fail:

rx.operators.OperationZip$UnitTest > testAggregatorUnsubscribe FAILED
    java.lang.NullPointerException at OperationZip.java:611

Not sure how I missed it when I reviewed the previous commit … but I did.
Merge pull request #133 from benjchristensen/fixes

Various fixes
Update language-adaptors/rxjava-scala/README.md
Update language-adaptors/rxjava-clojure/README.md
Update language-adaptors/rxjava-clojure/README.md
Update language-adaptors/rxjava-groovy/README.md
Update language-adaptors/rxjava-jruby/README.md
Update language-adaptors/rxjava-scala/README.md
Create CHANGES.md
Adapt Groovy VideoExample to Clojure