rename f.appendKeyValue to printKeyValue
rename f.appendKeyValue to printKeyValue

printKeyValue is working similar like printColored, not using
any fields of TextFormatter, should be a util func instead of
a method of TextFormatter.

Signed-off-by: Derek Che <9a876b0e626a7e524926f129e2e0ea9c4c104ff4@yahoo-inc.com>

dpatel06/logrus,dradtke/logrus,nicescale/logrus,w4ngyi/logrus,hvnsweeting/logrus,zbindenren/logrus,brandur/logrus,yxd-hde/logrus,torfuzx/logrus,noironetworks/logrus,penhauer-xiao/logrus,axiomzen/logrus,rfsbraz/logrus,alecha/logrus,snowsnail/logrus,tianon/debian-golang-logrus,noxiouz/logrus,cgag/logrus,freeformz/logrus,Barberrrry/logrus,chendrak/logrus,ConnectedHomes/logrus,devopstaku/logrus,therealbill/logrus,penhauer-xiao/logrus,marcosnils/logrus,HideoYamauchi/logrus,pippio/logrus,yawn/logrus,ineiti/logrus,creack/logrus,akutz/logrus,upstartmobile/logrus,sirupsen/logrus,wallclockbuilder/logrus,seatgeek/logrus,TheQuestionru/logrus,orvice/logrus,Invacio/logrus,Arkan/logrus,Dal-Papa/logrus,derekdowling/logrus,lixin9311/logrus,flowhealth/logrus,sirupsen/logrus,weekface/logrus,ryanfaerman/logrus,xyliuke/logrus,henrylee2cn/logrus,EmileVauge/logrus,gogap/logrus,Sirupsen/logrus