severity-aliases: add serilog 3 length aliases

See:
https://github.com/serilog/serilog/blob/653260089620944516cbd874449f3c4bd02edc0e/test/Serilog.Tests/Formatting/Display/MessageTemplateTextFormatterTests.cs#L42

Signed-off-by: Attila Szakacs <[email protected]>

Author: alltilla

lib/severity-aliases.table

@@ -40,11 +40,16 @@ alert,		SYSLOG_SEVERITY_CODE(1)
 crit,		SYSLOG_SEVERITY_CODE(2)
 critical,	SYSLOG_SEVERITY_CODE(2)
 fatal,		SYSLOG_SEVERITY_CODE(2)
+ftl,		SYSLOG_SEVERITY_CODE(2)
 err,		SYSLOG_SEVERITY_CODE(3)
 error,		SYSLOG_SEVERITY_CODE(3)
 warning,	SYSLOG_SEVERITY_CODE(4)
 warn,		SYSLOG_SEVERITY_CODE(4)
+wrn,		SYSLOG_SEVERITY_CODE(4)
 notice,		SYSLOG_SEVERITY_CODE(5)
 info,		SYSLOG_SEVERITY_CODE(6)
+inf,		SYSLOG_SEVERITY_CODE(6)
 log,		SYSLOG_SEVERITY_CODE(6)
 debug,		SYSLOG_SEVERITY_CODE(7)
+dbg,		SYSLOG_SEVERITY_CODE(7)
+vrb,		SYSLOG_SEVERITY_CODE(7)