Adding Difficulty Levels to Demo

Main Change: - Difficulty levels added: "Easy" and "Normal." Normal is the original difficulty level, while Easy includes many changes to make the game more accessible!

Other Changes: - The hitbox of the Cat Bait head area has been slightly reduced. - The "Fast Paws" upgrade has been changed. It can now only be taken once but provides a +12% movement speed boost immediately. The chance of this upgrade appearing in the selection has been reduced. - Mage Mice have been nerfed. They now take longer to create a fireball, and if you kill them before it appears, the fireball will not spawn. - Shaman Cat has been buffed. The starting damage is increased to 12, and its effect on size has been improved. Each upgrade now adds +40% to size. - Bodybuilder Cat has been buffed. Now its anvils can't fall in the same spot (where the Bait Cat is located), as a minimum radius around the cat has been added where anvils cannot drop. - Archer Cat has been changed. Its Multi-Shot can now hit a single enemy with all arrows if there are no others in the area. The base damage and fire rate have been slightly reduced. - The cost of Health Increase in Meta Enhancements has been changed. It now follows an arithmetic progression instead of a geometric one, reducing the total required sum for all levels by more than 50 times. - The base cost of Damage Increase in Meta Enhancements has been reduced.