Add option for outputting to JSON

[mattpocock]

This would be great for building tools with Lucy - for instance a browser-based visualiser.

[matthewp]

Is there a standard format for what this JSON looks like? Are there any existing tools that consume the JSON format?

[mattpocock]

@matthewp None - I'm imagining that for now, we'd copy the XState format (i.e. the first argument to createMachine) in JSON form.

[tonivj5]

if lucy exports a xstate machine, we could use its visualizer out-of-the-box, couldn't?

[mattpocock]

I'd prefer to output to JSON so that you wouldn't need an intermediate Babel transpilation step.