[Sprint: 40] XD-2425: Support RFC5424 SYSLOG Format

JIRA: https://jira.spring.io/browse/XD-2425

Add `--rfc` property; default 3164; can be 3164 or 5424.

Also add `nio` option (false default). nio should be used when many
connections are expected. Previously nio was always used.
oops; no