Invaders UPDATE

so I fixed some things in the code and made the invaders move down/shoot with different sounds. I also added a score and a saucer that gives you extra points.
It has a glitch so if you kill all the invaders just hit reset and it should start again with the same score and number of lives you ended with so you can continue shooting as if it's a new level.

Move cannon with left and right arrows, shoot with space bar.