*) updateImage() now takes invalidated as a parameter
*) added example of how to dynamically generate images
Update backlog.md
Update backlog.md
Make sure image are loaded before purging.

Using multiple web workers to load image could cause unloaded images to
be purged. This commit adds a filter before reordering.
Use Int16Array instead of Object array for LUTs and uses positive indexes.

This results in 4x speedup of the storedPixelDataToCanvasImageData and
probably 12x speedups for storedColorPixelDataToCanvasImageData.
GenerateLut should also be much faster.
Merge branch 'fix/cachePurgeUnloadedImages' into myplayground