A more generic logging interface

Hey all,

In Go logging is not simple. Every team and project ends up having their own idea and theory on what logs are and the purpose they serve.

I propose that instead of the current logging interface (which is really low level and wraps a subset of stdlib log.Logger) gocql should use a logging interface like this:

type BetterLogger interface {
  // some logging libraries want the underlying error instance
  Error(ctx context.Context, err error, args ...interface{})
  Errotf(ctx context.Context, err error, format string, args ...interface{})
  Info(ctx context.Context, args ...interface{})
  Infof(ctx context.Context, format string, args ...interface{})
}

This better encapsulates the idea of what log information would actually be presented. It also leaves implementation for something other than the standard library as a trivial effort.

Ex impl for stdlib log.Logger:

type stdLogger struct{}

func (s stdLogger) Error(ctx context.Context, err error, args ...interface{}) {
  result := fmt.Sprintf("error: %v", err)
  args = append([]interface{}{result}, args)
  log.Println(args)
}

func (s stdLogger) Errorf(ctx context.Context, err error, format string, args ...interface{}) {
  args = append([]interface{}{error}, args)
  log.Printf(format, args)
}

func (s stdLogger) Info(ctx context.Context, args ...interface{}) {
  log.Println(args)
}

func (s stdLogger) Infof(ctx context.Context, format string, args ...interface{}) {
  log.Printf(format, args)
}