feat(TU20/21): Implement la's TU21 patch file

This adds the following:

TU20:
1. Librarians now have a small chance to offer name tags for sale
2. Witches can now spawn at light level 7 or less in any biome or cave
3. Skeletons & Wither Skeletons now rarely spawn anywhere in the Nether

TU21:
1. Minecart entity limit increased

Minecraft.World/LivingEntity.cpp

@@ -259,9 +259,16 @@ void LivingEntity::baseTick()
 	}
 
 	// If lastHurtByMob is dead, remove it
-	if (lastHurtByMob != NULL && !lastHurtByMob->isAlive())
+	if (lastHurtByMob != NULL)
 	{
-		setLastHurtByMob(nullptr);
+		if (!lastHurtByMob->isAlive())
+		{
+			setLastHurtByMob(nullptr);
+		}
+		else if (tickCount - lastHurtByMobTimestamp > 100)
+		{
+			setLastHurtByMob(nullptr);
+		}
 	}
 
 	// Update effects