Life System, infinite ammo for primary fire and more!

On this new version 0.5.0 of the game the following features have  been added:

• Created a life system for enemies, where some of them will take 2 or 3 shoots to kill them. This way there are enemies that are more dangerous than others.

• Primary fire has now infinite ammo and the power up of ammunition has been replaced for another one that grants multiple shoots for primary fire during some time.

• Firerate increased for primary fire to compensate that now some enemies can take more than one hit.

• You can no longer take the shield if you are already shielded. This way it's not possible to waste the power up.

• With the life system, squares have become more dangerous, so the spawn chance of them has been reduce for game balance.

• Some collisions masks have been corrected.