Define generators for our JSON type

[GerardvSchie]

For automated testing it would be useful to have generators

Probably best to generate haskell code equivalent next to it so we know what result to expect
F.e generate these two in the same generator. We take the Haskell as expected and json as result.
JSON: JsonObject $ Map.singleton "+" (JsonArray [JsonNumber 1, JsonNumber 2])
Haskell: ((+) 1 2)

Also keep in mind that some need numeric json as parameters whilst others need booleans.
So generatorNumericJson
generatorBoolJson
generatorStringJson

are some of the generators to expose for testing purposes