code: func (fi *FieldInfo) PutAttribute(key, value string) string {
  	if fi.attributes == nil {
  		fi.attributes = make(map[string]string)
  	}
  	var v string
  	v, fi.attributes[key] = fi.attributes[key], value
  	return v
  }
docs: /*
  Puts a codec attribute value.
  
  This is a key-value mapping for the field that the codec can use to
  store additional metadata, and will be available to the codec when
  reading the segment via Attribute()
  
  If a value already exists ofr the field, it will be replaced with the
  new value.
  */