New features, as requested

Version 1.56.0 contains a number of enhancements that were requested by players via the contact form and quick survey:

• A swipe action can be used to select any group of squares that does not contain a block. Actions can then be performed on these squares together, such as number elimination.
• Pencil mode includes the possibility to set temporary blocks. This can be useful for trying out possible block positions.
• Pencil mode stays on when squares are selected by tapping a hint. Updates to multi-selected squares are also possible with pencil mode still active.
• When the last pencilled candidate has been eliminated from a square, the square shows the outline of a block, instead of appearing empty. This is to indicate that the square might be ready to receive a block, because no candidate values are left.
• The difficulty weighting for the puzzle generator can be configured in more diverse ways. Players can now mix and match the weights for the different categories of difficulty.
• When the difficulty weighting is set exclusively to either "harder puzzles" or "easier puzzles", the generator is more likely to generate puzzles that have maximum or minimum difficulty.
• Fix for a rare issue where the sum combinations were occasionally not being displayed correctly after being inverted.