Scale and Flip facilities

I have now added scale and flip facilities, to allow the same image to be used for a sprite at different sizes and reversed.

Different scale in x and y direction is possible, invert, mirror and all three.

In the diagram:
1. Normal sprite
2. 75% scale on both x and y axes
3. 75% scale on both x and y axes plus mirror
4. 75% scale on both x and y axes plus mirror plus invert