Crosserville Toolkit Extension

Adds extra tools for grid construction on Crosserville.com. The current toolset includes: - Flipping the grid horizontally, vertically, and diagonally. - Rotating the grid. - Flipping the contents of across or down slots. - Button in Fill pane for accepting fill for single-option cells (grey) - Button in Fill pane for accepting a single slot in the suggested fill. Click on the extension icon (pin it, if it's not visible) to activate/deactivate the toolkit. The code and latest version are available at https://github.com/sdbrody/crosserville-toolkit