Timeout doesn't close socket connection

Hi guys!

I was struggling some time on automatically closing the `fluent` socket when idling.
I wanted to emit some logs and then let the process to exit. That never happened, because the internal `fluent` socket was still open.
I could just call the `end()` function, but that was not an option for me.

After studying [Node.js socket documentation](https://nodejs.org/api/net.html#net_socket_settimeout_timeout_callback) I found out that calling `socket.setTimeout` doesn't really close the connection, only emits a `timeout` event which then needs to be handled by the developer.

That was of course my lack of knowledge, but I'm thinking how `fluent-logger-node` could be improved here.

What do you guys think of emitting the `timeout` event on the `FluentSender` and let developer call `end()` method later?

The other option would be adding e.g. `autoClose` or `closeOnTimeout` boolean flags to the `FluentSender` constructor.

Also I figured that in `tls` mode, the given `timeout` is not set on the `socket` (even `{ tlsOptions: { timeout: 3 } }` doesn't work).

For now I use a workaround:
```javascript
fluent.on('connect', () => {
fluent._socket.setTimeout(1000)
fluent._socket.on('timeout', () => {
fluent.end()
})
})
```

Thanks for feedback. Sorry if I misunderstood the problem and there is some other way to handle that.