Feature: add has_many through

[watzon]

For some of my projects I tend to use join tables quite a bit, but not having the ability to do has_many Record, through: OtherRecord makes it pretty difficult to do that in a nice way. RethinkDB does have table joins, so I'd think it would be possible.

[caspiano]

I don't currently have a use for this feature but it would be a good one. Feel free to jump on this.

[watzon]

I've been trying to work it out, but it's proving more difficult than I thought. I'll think on it some more and try to get something rolled into a PR.