We should provide a standard structured logger interface which consumers can inject with an implementation. zipkin-go-opentracing uses an interface compatible with the Go kit logger interface which seems the best candidate.

type Logger interface {
	Log(keyvals ...interface{}) error
}

This will allow people to easily fetch the K/V pairs coming from errors and exceptions within the library and merge them with their application logging infrastructure.

For people not liking structured logging we should provide an adapter for the standard Go log.