docs: function winstonFormatter (options) {
      // get callsite to for filename:linenumber where logger was called
      var callsite = callsites()[10]
      // string to log
      return options.level + ': '
          + (typeof options.message === 'string' ? options.message : '' )
          + ' (' + callsite.getFileName() + ':'
          + callsite.getLineNumber() + ':'
          + callsite.getColumnNumber() + ')'
          + (typeof options.meta === 'object' && Object.keys(options.meta).length ? '\n\t'+ JSON.stringify(options.meta) : '' )
  }