code: func (l *Logger) With(keyvals ...interface{}) *Logger {
  	return &Logger{
  		Output: l.Output,
  		Info:   log.With(l.Info, keyvals...),
  		Trace:  log.With(l.Trace, keyvals...),
  	}
  }
docs: // A logging context (see go-kit log's Context). Takes a sequence key values
  // via With or WithPrefix and ensures future calls to log will have those
  // contextual values appended to the call to an underlying logger.
  // Values can be dynamic by passing an instance of the log.Valuer interface
  // This provides an interface version of the log.Context struct to be used
  // For implementations that wrap a log.Context. In addition it makes no
  // assumption about the name or signature of the logging method(s).
  // See InfoTraceLogger