Implemented GetIterator operation
Merge branch 'getiterator' of git://github.com/mairbek/RxJava into GetIterator-review
Refactored Iterator implementation out of Observable into OperatorToIterator

- Trying to keep the massively large Observable.java class focused on the API and implementation details off in small classes.
Merge pull request #178 from benjchristensen/GetIterator-review

Review and Refactor of GetIterator