Add adapter for GO obo-json format

[cmungall]

Note that in GO have a proposed JSON representation of OBO that would obviate the need for special purpose parsers. Your comments as a developer of an obo parser would be most welcome:

• https://github.com/geneontology/obographs/
• https://douroucouli.wordpress.com/2016/10/04/a-developer-friendly-json-exchange-format-for-ontologies/

In theory adoption of this json would lead to more robust and easier to write parsera

Feel free to close this issue if you think it's not relevant.