Added Bomber, Bug fixes, Faster Enemies

Player can no longer stack upgrades. Used to work well with machine gun where you would collect a second machine gun upgrade before the current one ran out allowing you to shoot 2 bullets at the same time. Could stack up to as many as you like.

You can now save your laser charge. If you are running out of time on the laser upgrade you can now prolong it by collecting another laser powerup before the current one runs out and it won't reset the current charge.

Bomber added: very fast speed, 5 health, 0 collision damage, 3 explosion damage, explodes on collision with player or on death, explosion deals damage to player and enemies within a certain radius.

Menu updated: options to lower volume, set fullscreen, and disable the lighting effects.

Bullets no longer get stuck on enemies and other bullets.