Adding image and extras

[abetusk]

I'm not sure if you want to merge the features I added but in case you do, here's the PR.

The main feature is adding an image for the moon. I used an image I got from Wikipedia (credit and license information in the CREDITS.md file).

I've also added some command line features and a help screen describing the new options. Running python3 main.py -h gives the following:

Lunar Calendar generator
Version: 0.2.0

usage:

  python3 main.py [-h] [-v] [-y year] [-E] [-M] [-S] [-F] [-o output_file] [-i moon_image] [year]

    -y year         Year to generate
    -o output_file  Output HTML (default 'lunar_calendar_YEAR.html')
    -M              Use moon image
    -E              Enhance new, full, black and blue moon images with colors (image only)
    -S              Succinct (remove footer and new/full moon dates)
    -F              Remove only the footer
    -i moon_image   Moon image to use ('data/supermoon_l3_bw_s.png')
    -h              Help (this screen)
    -v              Print version

Some example usages along with their images:

python3 main.py -M 2025:

python3 main.py -c 'rgb(32,32,32)' -E -M 2025:

Normal usage should remain unaffected. For example, running python3 main.py 2025 should give the same result as before.

I had to hack the blue, full, new and black moon SVG overlays and so they might be pretty specific to the image. It's a pretty subtle feature to begin with and I only fiddled with it for the image portion.