Remove Gson dependency and PureeLog interface

[VictorAlbertos]

This PR removes Gson dependency from Puree and replaces the types used for representing the serialized JSON, JsonObject and the JsonArray, by String and List<String> respectively. After doing this change, PureeLog was of no use so it has conveniently been removed.

The instrumentation tests, as such as the demo project and the docs, have been properly updated to reflect the latest changes

[VictorAlbertos]

@k4zy this is the PR that I said I would open :)

[wraitho]

I'm not sure how many consumers this library has, but one thing to keep in mind that Victor's changes are breaking changes for the consumers of this library so if this is merged then Cookpad Global team and if the Japanese App uses it then you also need to add the Serializer. (and any other consumer)

Other than that, I think it looks good!

[VictorAlbertos]

The main breaking change is the removal of the PureeLog interface: the clients of the library need now to stop implementing it. If this is not acceptable, I can keep the PureeLog interface as part of the API, even though it does nothing internally in the library.

The new requirement of supplying a serializer is easily solved in the case of Gson, as it is explained in the updated README:

public class PureeGsonSerializer implements PureeSerializer {
    private Gson gson = new Gson();

    @Override
    public String serialize(Object object) {
        return gson.toJson(object);
    }
}

From my point of view, the concrete implementation of the serializer should not be the responsibility of Puree. If you think that clients will benefit from shipping a PureeGsonSerializer, to avoid to have writing the above code, I can create another Gradle module called gson-serializer (as Puree core can't longer depend on Gson) and put there the PureeGsonSerializer.

[wraitho]

Looks good :)

[mbarta]

LGTM

[mbarta]

What's the reason for catching JsonException and re-throwing RuntimeException here? Also, the method's signature specifies it throws JsonException

[VictorAlbertos]

Because this is Java and that's a checked exception so it's forced me to re-trow with an unchecked exception 🤷‍♂️

[VictorAlbertos]

Thanks for the reviews!