Added Difficulty

I didn't do much today. I just added more difficulty and fixed a bug.

• More turrets spawn, the higher your score. Newer turrets shoot faster.
• Once passing a score of 100, turrets will shoot faster for every point you get.
• Removed code that was meant to test stuff. In version 1.0.0 you could press and hold “L”, and the turret would shoot out a bunch of bullets.