what about add property for event.categoryName ? #1

Hi.

In the current version, although event has property 'categoryName', which is defined the parameter of getLogger(), there's no property in output data that is defined by the categoryName. What about to add the following line in the returned function of function logstashHTTPAppender(config) ?

{
  message: format(event.data),
  context: event.context,
  level: event.level.level / 100,
  level_name: event.level.levelStr,
  category_name: event.categoryName, // +
  channel: config.logChannel,
  datetime: (new Date(event.startTime)).toISOString(),
  extra: {},
},