caching in ontol_factory.py

[saramsey]

On line 163 of https://github.com/biolink/ontobio/blob/master/ontobio/ontol_factory.py, there is code for retrieving the ontology from a cache.

Would it be possible to have an optional argument to the factory constructor (or the create method) to turn off this caching? That would be helpful to our work on KG2. Currently we do not want caching in our build process, so our only way to avoid this is to convert to JSON and then load the JSON file. Would be helpful if we could disable the built-in caching for when we are loading an OWL file.