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 
really, it's okay.. but there's a white space on line 29 that should be removed and lines 28-34 may be organized like that.. or maybe i'm wrong xD

<pre><code>local travelNode = keywordHandler:addKeyword({'darashia'}, StdModule.sayTravel, {npcHandler = npcHandler, onlyFocus = true, text = 'Do you seek a passage to Darashia for %s?', cost = 60, discount = postmanDiscount})
	local childTravelNode = travelNode:addChildKeyword({'yes'}, StdModule.say, {npcHandler = npcHandler, onlyFocus = true, text = 'I warn you! This route is haunted by a ghostship. Do you really want to go there?'})
		childTravelNode:addChildKeyword({'yes'}, StdModule.travel, {npcHandler = npcHandler, premium = true, level = 0, cost = 60, discount = postmanDiscount, destination = getDarashiaGhostPosition})
		childTravelNode:addChildKeyword({'no'}, StdModule.say, {npcHandler = npcHandler, onlyFocus = true, reset = true, text = 'We would like to serve you some time.'})
	travelNode:addChildKeyword({'no'}, StdModule.say, {npcHandler = npcHandler, onlyFocus = true, reset = true, text = 'We would like to serve you some time.'})
</code></pre>