Day 2 and 3: Added doors, collision detection for projectiles and improved some other little things

The game now has 3 doors which will open when another goblin enters or close if the goblin has already entered. Also, the player can now shoot projectiles. Collision detection has been implemented for the fired projectiles. (Point-Line collision). The next step will be to add collision detection for the player (Mr. Clean), so that he can't walk over furniture or walk off the screen. After this step has been accomplished I'm going to add the Goblins, which will be the hardest part, but the most challenging, in my opinion. And after all that I'll clean up my code before I do anything else =).