Support domainIncludes and rangeIncludes

Hi!

A couple of things: really like the library! I also saw you are on vacation until 2018 (enjoy!), so no expectations of urgency here. So I've been using you're library to build a GraphQL API based on an ontology, while using your [aquest repo](https://github.com/dherault/aquest) as a guideline. As part of my ontology I would like to extend some schema.org classes, but I ran into a problem there. I was able to include their ontology, but it uses `schema:domainIncludes` and `schema:rangeIncludes` to indicate relationships between classes. I did some work on Google and found a discussion about the subject [here](https://github.com/dbpedia/ontology-tracker/issues/14), which seems to indicate that the `Includes` version is preferable, although I imagine supported both should be easy enough as well. Any thoughts on the matter? Would be happy to help out with a PR.