Please add an ability to scale sprites.

[mkondel]

I would like to add a spritesheet and be able to scale it as an HTML <img>. The current version creates a <div> with the image data as a CSS background-image property. The 'height' and 'width' parameters for sprites will change what part of the spritesheet it will display. Scaling using CSS transform: scale(0.5) introduces strange behavior where the images will have thick padding. This is also what #6 seems to want too.