Add documentation for use with feathers-hooks

[daffl]

As came up in the issue at feathersjs-ecosystem/feathers-hooks#23, modifying the Mongoose models this adapter returns in a hook can cause some unexpected behaviour. We probably want to add some documentation and with Feathers 2.0 some hooks in this repository that help dealing with this.

[marshallswain]

Here's what I think this needs:

• A configurable toObject hook.
• Docs.

I think other hooks can be added later, but this one's pretty important, IMO.
http://mongoosejs.com/docs/api.html#document_Document-toObject

[ekryski]

Agreed. We also might see some nice patterns emerge with some of the other ORM adapters coming out soon.

[ekryski]

This was closed with PR #33.