Test: JSON Roundtrip

[dxo]

It would be cool to have some quickcheck tests that:

1. Generate some behaviours
2. Write those behaviours to JSON
3. Parse the JSON into a behaviour
4. Assert equality of the parse behaviour to the original

To do this we would need to implement FromJSON instances in RefinedAST, which adds some complexity, but it probably required anyway if we want to allow external tools to programatically generate act.