XD-140 Parameterize Syslog Port; Support TCP

- Rename syslog.xml to syslog-udp.xml
- Add syslog-tcp.xml
- Parameterize port

At this time, the protocol cannot be parameterized because of
context lifecycle issues (see XD-142).

- Add documentation for the syslog source:
	https://github.com/SpringSource/spring-xd/wiki/Sources#wiki-syslog