Implement MoP Guardian dynamic armor multiplier from mastery (Fixes #219)

Author: raethkcj

libs/StatLogic/Mists_Logic.lua

@@ -859,11 +859,11 @@ if addon.class == "DRUID" then
 				["aura"] = 33891,
 				["group"] = addon.ExclusiveGroup.Feral,
 			},
-			-- Passive: Mastery: Nature's Guardian
-			-- TODO: Get value from tooltip?
+			-- Passive: Mastery: Nature's Guardian (Bear Form)
 			{
+				["aura"] = 5487,
 				["known"] = 77494,
-				["value"] = 0.16,
+				["mastery"] = true,
 			},
 			-- Buff: Moonkin Form
 			{

libs/StatLogic/StatLogic.lua

@@ -1166,6 +1166,11 @@ addon.StatModValidators = {
 			["PLAYER_LEVEL_UP"] = true,
 		},
 	},
+	mastery = {
+		events = {
+			["UNIT_STATS"] = "player",
+		},
+	},
 	meta = {
 		validate = function(case)
 			return case.meta == equipped_meta_gem
@@ -1479,6 +1484,8 @@ do
 		elseif case.tooltip then
 			local aura = StatLogic:GetAuraInfo(case.aura, false, case.exact)
 			newValue = aura.tooltip
+		elseif case.mastery then
+			newValue = GetMasteryEffect() / 100
 		end
 
 		if newValue then