put the palette stuff into pixel-bitmap.el because its not that much
experiment with channel based approach instead of palette based

- just kept things like they are for now, too much work I don't want to
  do right now
add an array overlay to editor
remove palette dep from pixel-editor-create
pixel-source-replace to update buffer with new pixels
match optional format in regex, put array begin and end in origin
fix pixel-edit-create still called with palette arg
fix editor not found in other buffers
modify pixel-mapx to call mapping function with n = nth iteration