Add optional syslog logrus hook (#343)

* add optional syslog logrus hook

* document syslog

vendor/gopkg.in/mcuadros/go-syslog.v2/format/rfc5424.go

@@ -0,0 +1,17 @@
+package format
+
+import (
+	"bufio"
+
+	"gopkg.in/mcuadros/go-syslog.v2/internal/syslogparser/rfc5424"
+)
+
+type RFC5424 struct{}
+
+func (f *RFC5424) GetParser(line []byte) LogParser {
+	return &parserWrapper{rfc5424.NewParser(line)}
+}
+
+func (f *RFC5424) GetSplitFunc() bufio.SplitFunc {
+	return nil
+}