Comment: mongo query parser

I just wanted to mention to you guys that I wrote a module related to what you're doing (tho with different goals): [mongo-parse](https://github.com/fresheneesz/mongo-parse). I wrote it to be able to parse a query allowing you to map one query into another (originally for the purposes of turning string _ids into ObjectIDs). Thought you guys might be interested in taking a look at it, and if you ever decide to refactor your code, it would probably simplify your internals.

Start by reviewing the linked mongo-parse module and comparing its query-mapping approach with this repository's current internals. The issue does not identify files, tests, or a specific requested change; done would require a maintainer decision about whether a refactor is wanted and what scope it should have.

Written by the indexing model from the issue text.