Update keywords.txt

Author: thijse

keywords.txt

@@ -18,6 +18,7 @@ fatal	KEYWORD2	fatal error output
 error	KEYWORD2	error output
 warning	KEYWORD2	warning output
 notice	KEYWORD2	info output
+trace 	KEYWORD2	trace output
 verbose	KEYWORD2	verbose output
 begin	KEYWORD2	initialize library