Completed Task 10

In game.js, the OBJECT_POWERUP is already defined. Create these
"powerups" that drop randomly from the top of the screen. Create sprites
for these "powerups" and add them to the sprite sheet. (Your art skills
won't be judged. The Paint app for Windows is good enough for making
this edit.)
Invincible star: makes any player ship that collides with it invincible
for 5 seconds. The player ship should blink to indicate current
invincibility.
Poison pill: any ship (player or enemy) that collides with it dies.