Add correlation to logs

[madshov]

Hi!
I would be nice to be able to add a correlation-id per request to all logs including the ones created in ServeHTTP method. Currently errors returned from an endpoint will not have any correlation-id:

response, err := s.e(ctx, request)
if err != nil {
	s.logger.Log("err", err)
	s.errorEncoder(ctx, err, w)
	return
}

It could just be the request-id from the context. I don't see how it's possible to add it in these cases. If it can be done, I would appreciate, if you would let me know.

[sagikazarmark]

After #863 is merged, you will be able to put correlation information into the context and use it in the error handlers.

[madshov]

This is now possible in v. 0.9.0 using a custom error log handler.