def level_mapping=(mapping)
      case mapping.to_s.downcase
        when 'logger'
          @level_mapping = GELF::LOGGER_MAPPING
        when 'direct'
          @level_mapping = GELF::DIRECT_MAPPING
        else
          @level_mapping = mapping
      end
    end
def level_mapping=(mapping)
      case mapping.to_s.downcase
        when 'logger'
          @level_mapping = GELF::LOGGER_MAPPING
        when 'direct'
          @level_mapping = GELF::DIRECT_MAPPING
        else
          @level_mapping = mapping
      end
    end
+mapping+ may be a hash, 'logger' (GELF::LOGGER_MAPPING) or 'direct' (GELF::DIRECT_MAPPING).
 Default (compatible) value is 'logger'.