New features on Npc Lib and three npcs using this features

Now we can finally have postman discounts( 10 gp ) and new frontier
discount( on brodrosch, 50 less gp ) and another thing i have done is
removed some creatureSayCallback( they are overly used on things that
can be done with keywordHandler:addKeyword )

Cheers @xWhiteTiger @ninjalulz 
please remove this tab xD good work :+1: