Acrostic look-and-feel

We have added support for Acrostic puzzles (wikipedia) to Crosswords.

Acrostic puzzles have a grid that is separated into two parts: First the main grid, which contains a long quote. Next, there are a set of clues, with a separate one-line grid for each clue. The cells of the main grid are numbered, and each cell in the clue grids also has a number associated with it. The cells are shared: guessing in the clue grid will put its letters in the main grid, and guessing in the main grid will also fill out the clues. The description at wikipedia is pretty good for understanding it.

The puzzle is solved through a combination of guessing in the clues, and guessing in the main grid. Here's an image of a pen-and-paper acrositc: