Add feature: Add dither filter for color halftoning.
Fix bug: CanvasImage is throwing an error when cloning ImageData
Fix bug: Halftone filter is not considering threshold argument
Fix bug: Halftone filer is considering default threshold to be 125

	modified:   smp/bitmap/DistributionFilter.js
	modified:   smp/bitmap/ProcessImageData.js
	modified:   smp/canvas/CanvasImage.js