Alpha Version 4

Main changes:

• Added a new weapon: Gray Goo. Gray Goo multiplies whenever it hits an enemy!
• Added a public leaderboard where players can save their scores.
• Added a new ship module: Emergency Healing System. This can be used to bring you back from the brink of death.
• Added a new enemy that wields a deadly laser cannon.
• Added one more level to the game.
• Increased the spawn rate of asteroids.