Support custom format using patterns in SyslogLayout

It would be nice to be able to appy custom format to a message sent using SyslogLayout, user will be able to use PatternLayout/XMLLayout, etc... and format it as a syslog message (add syslog header ).

so the usage would be :
<SyslogWrapLayout facility="lpr">
<PatternLayout pattern="%d

[%t] %marker.%-5level %logger

- %msg"/>
</SyslogWrapLayout>