Updating include syntax to support hasAndBelongsToMany relationships

I hope this is a minimally invasive change to support hasAndBelongsToMany relationships when using the `include` style syntax. I dangle an additional reference on the relation model, `modelThrough` and use that in the include logic; branching to a second `include` call or to returning a normal `modelTo.all` callback.

I also handled all the jshint errors I was getting in `lib/include.js`.