feat(zip): Adding handler to return a zip object to the client.

[DSchrupert]

Since we don't pass the exchange to the handler to populate response headers.. i needed to add a new one to ensure the right content type & dispositions are used.

Let me know if there's anything i should change.

In regards to: networknt/light-codegen#112

Thanks

[DSchrupert]

@stevehu what i also noticed in this approach (of not having the handlers responsible for the response headers) is that they can no longer return errors to the client if the RpcRouter is always expecting a file...
I think we might want to reconsider the handler interface parameters.
Thoughts? Am i missing something?

[stevehu]

You are absolutely right. We should pass the exchange to handlers so that they can set headers or respond errors based on business logic. Since the entire portal and most of networknt services are depending on it. Let's think through it and make all changes in one shot. Let me come up an impl in a branch and we can chat about the pros and cons. Or you can take an initiative if you have time. My entire next week is planned already and I need a big chunk of time to do this.