Added NewSyslogBackendPriority method
Added NewSyslogBackendPriority method

mousesun/go-logging,giftig/go-logging,dkolbly/go-logging,ckeyer/go-log,nporsche/np-golang-logging,shell909090/go-logging,jbenet/go-logging,d-ulyanov/go-logging,zj8487/go-logging,yangzhao28/go-logging,s-kostyaev/go-logging,alecthomas/go-logging,op/go-logging