Minor Overhaul

Performed the only major update I plan on doing for this. Changes include:

• Improved maze generation
• Updated sprites for player and mines, as well as some minor animations
• Mines to blink visibly in the dark intermittently
• Ghost behavior is entirely different
• Addition of keys to open door to next level
• Added difficulty modes
  • Easy: no fog, entire maze visible
  • Normal: same as original, with fog clearing as you traverse the maze
  • Hard: You can only see your current field of vision.