Add an option to extract and print the metadata of an existing sonify movie file

[liamtoney]

sonify writes the version used to create an animation, and the specific Python function call itself (with params), to the artist and comment metadata tags in the video file.

For a given existing animation target.mp4, the following FFmpeg command prints just the version info (from artist tag):

ffprobe -loglevel quiet -show_entries format_tags=artist -output_format compact=nokey=1:print_section=0 target.mp4

likewise, this command prints just the specific call made to sonify:

ffprobe -loglevel quiet -show_entries format_tags=comment -output_format compact=nokey=1:print_section=0 target.mp4

Since this command requires only FFmpeg, we could make a wrapper around these two commands so that e.g. one could do

sonify --extract-version target.mp4

or something similar.