Remove function with query is missing: `destroyAll(cond)`

like here:
http://docs.mongodb.org/manual/reference/method/db.collection.remove/

Look at the MongoDB adapter in the jugglingdb codebase, likely under lib/adapters/. Find the existing destroy or remove methods. The issue references the MongoDB remove method documentation. Implement a destroyAll(cond) function that accepts a condition object and translates it to a MongoDB remove query. Check test files for the MongoDB adapter to see how other database operations are tested.

索引モデルが issue の本文から書いたものです。