Fixed Bullet & Shooting code
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character.h
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- Moved Bullet struct definition to "bullet.h"
- Added Ghost::isHitByBullet() to check for Ghost-Bullet collision

bullet.h
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- Bullet struct
	- Modified draw() to use gotoTileDown() correctly
	- Modified move() to remove redundant code
	- Added "collided" boolean to control deletion

game.h
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- Modified update() to implement code for controlling Bullet spawn and despawn
- Modified render() to draw and undraw Bullets

maps.h
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- Added a pointer to a Bullet "*shot" to control the Bullet in the map
- Modified constructor to give a default NULL value to "*shot"