update ETL README to reflect how the tests and implementations work
clojure etl - make data types for tests consistent with the README
elixir etl - make data types for tests consistent with the README
javascript etl - make data types consistent with the README
python etl - make data types consistent with the README
ruby etl - make data types consistent with the README
etl README - fix case in output to match the tests
Merge pull request #855 from etrepum/etl-readme-852

Rewrite ETL readme and use consistent data types in tests