Control Improvements
- Adds the ability to backtrack the current temporary chain
- Smaller sub-chains can now be deleted by right-clicking, allowing the player to fix issues without going back and undoing everything they've done
- Undo now deletes only the last chain that connects 2 valid numbers
- Adds trimming to the current temporary chain to remove non-numbered cells at the edges of the chain
- Adds a tutorial level explaining the improvements to the controls