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