Crosshair and Game Balance

A crosshair has been added in order to replace the windows cursor, now the game looks a little bit more like a shooter.

As https://itch.io/profile/tricky-fat-cat suggested in his comment:

Additionally, there isn't any way to restore ammo for the main weapon. I suggest increasing spawn rate for ammo pickups.

Power up spawning has been balanced in order to have more spawn of ammo and resources and less power ups that vanish after some time, like the speed or the invincibility.

The enemy speed has been slowered a bit at the start of the game to improve gameplay.