Modified code for level progression [WIP]
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main.cpp
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- Renamed gameLoop() to levelLoop() and moved to game.h

gameStage.h
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- Added gameLoop() that controls the whole gameplay aspect and calls levelLoop() for individual levels

globals.h
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- Moved all global variables to this header file

maps.h
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- Modified the Maps constructor to obtain a filename and generate filenames for .map and .aimap