2DShooter - Coursera project

This is the 2DShooter project for Coursera's course "Game Design and Development 1: 2DShooter".

I've added the following modifications relative to what was done in the classes:

1) Level 1 - it includes some black holes that do a circular movement, and when the player touches them, it dies instantly. I used one of the textures provided in the assets - for doing the circular movement, I had to write code;

2) Level 2 - after about 5 to 10 seconds of play time, we get asteroids coming in the direction of the player with random velocity. There are several spawner game objects that spawn these asteroids at random intervals. I used the existing asteroid texture. The player can shoot at the asteroids, but they don't count as an enemy. If an asteroids hits the player, he dies instantly.

3) Level 3 - added several black holes, using another of the provided textures in the asserts package, that behave like teleporters. If the player collides with one of them, it is instantly teleported to another location. After a teleport, the black hole will be inactive for 3 seconds - so to teleport again, we have have to wait at least 3 seconds.