0.3.9 "Blue In The Face"

This release adjusts BLUE_NOISE dither (like the previous release), but also changes the default palette from HALTONIC (made by a program) to AURORA (made by DawnBringer). There are also some small tweaks to defaults for thresholds on PaletteReducer.analyze() and related methods. BLUE_NOISE dither is now more subtle and keeps flat areas in input images more reliably; raising dither strength can reduce the flatness if desired. NEUE remains a great choice for realistic images and almost anything with smooth gradients, but BLUE_NOISE is targeted differently at pixel art and animations in particular.