Missing the ontology package dependecy

[maxnilz]

Hi, thanks for sharing the interesting implementation

I Just cloned this repo, and had a quick look, and found there is an ontology package import in the main athena.py while missing the implementation for that.

It seems like the ontology package is part of the implementation of this project instead of a separate public python package, so I'm Wandering if it's by design or by mistake. and if it's possible to populate the missing bit to fill the gap and make this project complete.

Many thanks.