code: func NewCustomMetricsSpec(config *config.Config) (*CustomMetricsSpec, error) {
  	var spec CustomMetricsSpec
  
  	err := config.UnmarshalKey("pitaya.metrics.custom", &spec)
  	if err != nil {
  		return nil, err
  	}
  
  	return &spec, nil
  }
docs: // NewCustomMetricsSpec returns a *CustomMetricsSpec by reading config key