tweak LIKE test to provoke type inference bug
preserve annotations for equal nodes (Fixes #220)
Fixes #206 by adding a new optimization pass that deletes unused fields.

1. add new file for optimizers in mongodb; create pipelinezipper and begin work on optimization to delete unused fields; prepare to move old optimizers into new package
2. delete old optimizer now that it's been relocated to new optimize package
3. got optimizer working for planner test cases, with updating test cases to reflect new behavior
4. add test case that was not passing before most recent optimization pass
quick update to readme
code cleanup
Fix test where limit was in wrong place.
Explicitly choose >>> or &&&.