feat: Add 4 methods (#158)

1:
Player:GetAchievementPoints

2:
Player:GetCompletedQuestsCount
This should have been GetCompletedQuestsCount, not sure how to update that now.

3: You also have an option to include feats of strength or not (not included by default, blizzard like)
Player:GetCompletedAchievementsCount

4: RegisterPlayerEvent
OnCreatureKilledByPet

src/ElunaLuaEngine_SC.cpp

@@ -806,6 +806,11 @@ public:
     {
         sEluna->OnBattlegroundDesertion(player, type);
     }
+
+    void OnCreatureKilledByPet(Player* player, Creature* killed) override
+    {
+        sEluna->OnCreatureKilledByPet(player, killed);
+    }
 };
 
 class Eluna_ServerScript : public ServerScript