Adds a bijected source/sink + test
Remove commented code, add better test case
Make the transformer be an implicit, clean up test with nicer code with that in place
Merge pull request #886 from twitter/feature/BijectedSourceSink

Add a bijected source sink which allows composing a bijection with a typedsink
Tiny fix to use an ImplicitBijection rather than Bijection
Add contraMap to the tuple setter, use from the new BijectedSourceSink
Merge pull request #887 from twitter/tinyFix

Tiny fix to use an ImplicitBijection rather than Bijection
Merge https://github.com/twitter/scalding into develop