version history of PixlePack plugins

v 0.02:
- added plugins: interlace
- some code optimization

v 0.01:
- plugins: compare, convolution, darken, deinterlace, difference,
  lighten, multiply, overlay, screen, shadowcaster, softlight
- KNOWN BUG: some artefacts due to rounding errors (as we are using 
  8bir values), especially in convolution