Enemies shoot!

As of v0.3a enemies can shoot!

There are two types of enemies, and each type has its own bullet type.

Bullets may seem round, filled geometric shapes, but in fact they have different speeds and different damage points.

Player can now receive damage from enemy fire.

Player's health status is displayed at the top-center of the screen.

Whenever the player kills an enemy, the Score and Health status are animated.

The following ideas are candidates for future updates:

-- larger battle space: it's a fundamental change. 

-- minimap (radar map): fundamental change. prerequisite: larger battle space.

-- powerups : rather simple to implement, but will make the code harder to navigate.

-- animated portal for enemies to spawn (maybe they have some roads from the top corner?)

-- enemies move towards player (A*?)

-- better sprites and background: trivial but I prefer working on the gameplay, rather than the aesthetics.

-- sounds!

Enjoy!