Added map scrolling, file structure change

- Map now scrolls on a background
- Detects edges: if player is close to an edge, the camera will stop
centering on the player
- Enemies fade while moving forward if they hit a player; they fade
while moving backward if they die by a bullet hit
- Pause screen is now transparent (shows game in background)
- Changed file structure to be easier to work with
- Optimized many methods, improved readability