Support Json reports

[dinesh-hd]

There is strong use case of Diffuse being run on CI Systems. CI Systems can then send JSON reports over to NOSQL data stores for data analysis.

[JakeWharton]

You can use the API to get back models which could then be serialized to JSON or converted to whatever shape of serialization you wanted. I'm not quite sure whether I want to commit to a stable output format in JSON form.

[dinesh-hd]

I can contribute if you think this feature aligns with your vision.