introduce error handling function

[muharem]

Currently there is not way to handle errors in case if sqs is not reachable.
In case of an error the lib writes log and write error to sqsErr subscriber field. That field is not useful for clients, since we can not read and reset it safely.
To provide an error handling for clients we introduce onErrorFunc which will be called if an error occurs.

[jsafoodpanda]

It seems extremely limited. Do you have an example of a practical use case?

[muharem]

It seems extremely limited. Do you have an example of a practical use case?

@jsafoodpanda
I suggesting this one instead of this #71
And in my opinion this more flexible way. Ideally the lib should not log errors and should return an error, since in this case its concurrent code we provide a way to inject a handler for an error.

[wilsont]

yes, inject a handler gives us more flexibility 👍