Levels update

• Rearranged some levels in w2 (2-3, 2-4, 2-5, 2-19 and 2-20) to be in order of difficulty.
  
• Changed w3?₁ to more detailed content.
  
• Adjusted the number of levels required to clear w5, which makes it impossible to skip the gimmick that first appeared in 5-21.
  
• Fixed 4-H, 0-ο₂ and A-F to prevent unintended solutions.