TODO.md

• Generate mines' location into a HashSet
• Generate the other field based on the location of mines
• Implement opening logic
• Refactor FieldState to reduce code duplication
• Add mechanism to indicate BOOM
• Add logic to indicate happy ending
• Add timer
• Add flags to fields
• Rewrite mine moving logic to change only field type, but not the state
• Rewrite FieldVisiter as Iterator if possible
• Create different methods for create mines and other fields
• Convert the static str errors into errorcode + static str