Fixes Mongoid Cursor Timeout Issue

This PR resolves #29 

Mongoid can timeout if it is iterating over a collection for longer than 10 minutes. I have encountered this when performing a Model.reindex! as our primary model pushes a lot of calculated attributes to Algolia. 

The method I've used to get around it is one referenced a few times in: https://github.com/mongoid/mongoid/issues/1334

i.e. manually batching through the collection