Gameplay Improvements

On this update I've been working on gameplay improvements.

After some gameplay improvements suggested by @tricky_fat_cat on various comments, I've been playing with the power up spawn system. Now the resources will be more abundant and it's not that easy to run out of ammo.

The enemies that were removed have been added again. The pink and yellow balls have been readded, but the yellow ball has been rezised because it was too big. Now the game feels better because there are more variety of enemies. Probably I will make two more versions for the triangles and the cubes, this way we have 3 enemy types of each geometric figure.

A Bug were you could shoot while the game was paused has been corrected.

I hope that the game feels better with this gameplay improvements!