Make happy ghasts move horizontally by W or S

Now, if you press W or S, the happy ghast will move in the direction of you eyes, which means when you are building in the air and your eyes are not looking at the block compleletly horizontally(like you are looking at the block a little downward), and then you move backward by pressing S, the happy ghast will rise up a little, then you have to adjust your eyes downward further to make the “+” still on the block; as this goes on, the happy ghast will move higher and higher and finally you have to make it move downward to build on. 

To solve this problem, we can make pressing W and S move horizontally, and use Ctrl to make it move downward.