New feature: Crop tool

This is a quick demonstration of the crop tool in action.

The crop tool is available since SpeedyPainter v2.7.0.

As you can see from the video, the tool is consistent with other canvas operations like canvas rotation, zoom or panning.
You can use the tool also to expand the current canvas size: useful when you realize that your whole drawing will go outside the current canvas area (a common mistake 😀 ).

Feel free to express your usage experience and suggestions.

Thank you! 🙂