Add command-line wrapper for Pyxelate.

[mdwelsh]

This PR adds a small wrapper around Pyxelate which can be invoked with the "pyxelate" command once installed.

Example usage:

$ pyxelate input.jpg output.png --factor 10 --palette PICO_8

Here is the full help message:

$ pyxelate --help
usage: pyxelate [-h] [--width WIDTH] [--height HEIGHT] [--factor FACTOR]
                [--upscale UPSCALE] [--depth DEPTH] [--palette PALETTE]
                [--dither {none,naive,bayer,floyd,atkinson}] [--sobel SOBEL]
                [--alpha ALPHA] [--noboost] [--quiet]
                INFILE OUTFILE

positional arguments:
  INFILE                Input image filename.
  OUTFILE               Output image filename.

optional arguments:
  -h, --help            show this help message and exit
  --width WIDTH         Output image width.
  --height HEIGHT       Output image height.
  --factor FACTOR       Downsample factor.
  --upscale UPSCALE     Upscale factor for output pixels.
  --depth DEPTH         Number of times to downscale.
  --palette PALETTE     Number of colors in output palette, or a palette name.
                        Valid choices are: ['TELETEXT', 'BBC_MICRO',
                        'CGA_MODE4_PAL1', 'CGA_MODE5_PAL1', 'CGA_MODE4_PAL2',
                        'ZX_SPECTRUM', 'APPLE_II_LO', 'APPLE_II_HI',
                        'COMMODORE_64', 'GAMEBOY_COMBO_UP',
                        'GAMEBOY_COMBO_DOWN', 'GAMEBOY_COMBO_LEFT',
                        'GAMEBOY_COMBO_RIGHT', 'GAMEBOY_A_UP',
                        'GAMEBOY_A_DOWN', 'GAMEBOY_A_LEFT', 'GAMEBOY_A_RIGHT',
                        'GAMEBOY_B_UP', 'GAMEBOY_B_DOWN', 'GAMEBOY_B_LEFT',
                        'GAMEBOY_B_RIGHT', 'GAMEBOY_ORIGINAL',
                        'GAMEBOY_POCKET', 'GAMEBOY_VIRTUALBOY',
                        'MICROSOFT_WINDOWS_16', 'MICROSOFT_WINDOWS_20',
                        'MICROSOFT_WINDOWS_PAINT', 'PICO_8', 'MSX',
                        'MONO_OBRADINN_IBM', 'MONO_OBRADINN_MAC', 'MONO_BJG',
                        'MONO_BW', 'MONO_PHOSPHOR_AMBER',
                        'MONO_PHOSPHOR_LTAMBER', 'MONO_PHOSPHOR_GREEN1',
                        'MONO_PHOSPHOR_GREEN2', 'MONO_PHOSPHOR_GREEN3',
                        'MONO_PHOSPHOR_APPLE', 'APPLE_II_MONO',
                        'MONO_PHOSPHOR_APPLEC', 'APPLE_II_MONOC']
  --dither {none,naive,bayer,floyd,atkinson}
                        Type of dithering to use.
  --sobel SOBEL         Size of the Sobel operator.
  --alpha ALPHA         Alpha threshold for output pixel visibility.
  --noboost             By default, adjust contrast and apply preprocessing on
                        the image before transformation for better results. In
                        case you see unwanted dark pixels in your image, use
                        --noboost.
  --quiet               Suppress logging output.

[sedthh]

Thanks man this is great!