Add Acrostic Puzzles to GNOME Crosswords

This project would start by extending a library called libipuz. This library loads and saves puzzles from the free ipuz file format. They would add support to load Acrostics from disk. Testing support will also be added. Once the files are loading, they would add support to the game itself through widget work. They'd have to write two custom widgets. First, they would write an answer widget that contains a sub-grid and links styles with the main grid. Then they'd modify the clue row widget for acrostics to support the different types of clues. As a final step, a separate widget will be written to add a custom layout for acrostics. Given those acrostics behave differently than crosswords, we want to lay them out differently. This can be done either by extending the existing custom widget, or them writing their own.