Added new HOOK_DESCRIPTIONOBJ and dialog_message/get_string_pointer functions (#181)

Added the second return value to HOOK_BARTERPRICE to modify the cost of the player's goods.
Fixed missing AC/DR mod stats when examining ammo in barter screen.
Added an option to display full item description for weapon/ammo in barter screen.

artifacts/scripting/sfall function notes.txt

@@ -491,6 +491,12 @@ Some utility/math functions are available:
 - redraws inventory list in the inventory/use inventory item on/loot/barter screens
 - invSide specifies which side needs to be redrawn: 0 - the player, 1 - target (container/NPC in loot/barter screens)
 
+> int sfall_func1("get_string_pointer", string text)
+- returns a pointer to a string variable or to a text
+
+> void sfall_func1("dialog_message", string text)
+- displays a message in the NPC response window in dialog or trade mode
+
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