Fluent send via UDP

Hi folks

I've tried to send logs to fluentd with this code
`from fluent import sender
logger = sender.FluentSender('app', host='127.0.0.1', port=24224)
logger.emit('test', {'from': 'localhost', 'to': 'fluentd'})
logger.close()
`

And success!
Now, do you have idea to send that via udp?
If it's already the feature, please write it on readme.md. I think I'm not only one who wants to send logs via UDP.

Thank you!

Start by reading the FluentSender usage shown in the issue and inspect the current sender implementation to determine whether UDP is supported. Check README.md for existing transport documentation; done means the project’s UDP capability, if available, is documented, or the requested UDP support has a clearly defined implementation and verification path.

索引モデルが issue の本文から書いたものです。