Don't open/close socket per message

[nkzawa]

Is your feature request related to a problem? Please describe.
The library opens and closes socket every time when a message is sent. It's very inefficient.

Describe the solution you'd like
Keep open socket and add the close method to explicitly closes sockets. Also add related events to Syslog class to be able to listen socket events.

Describe alternatives you've considered

Additional context
vercel#12 we already added the featured on our fork temporarily.

[syuilo]

any update on this?