Add graph for git tags

[roskakori]

Goals

• When a user specifies the command lines option --format=graph, the output is an image file showing how the SLOC changed over time for each git tag.
  • If the command line options for the source path are anything but a single git URL, pygount fails with the error:

    --graph requires a single git URL as source

  • The output image format is PNG.
  • The command line option --tags=REGEX allows to limit the tags to be analyzed to the ones matching the regular expression REGEX. The default is .*.
  • The order of tags to be analyzed is natural.
    • ℹ️ Use for example natsort.
    • ℹ️ This works best with semantic versioning.
  • The command line option allows to specify the colors for the most popular languages as comma separated list of hex codes with white space and # being ignored. ℹ️ For example: #123456, 789abc
    • The default is ❓ TBD: Use 8 colors that look "nice" but also alternate between bright and dark to make them easy to distinguish even for people with color deficiencies.
    • If less than 2 colors are specified, the option is rejected with the message:

      At least two colors must be specified.

    • If there are more languages than colors, the last color is used to sum up the additional languages as "Other".
      • The "Other" languages are always the bottom language, even if in sum they have more lines of code than the separate languages.
    • If there are more colors than languages, only the required number of colors shows in the graph.
    • ❓ TBD: How to handle a language that was part of the repo at some point but is not at the most version. For example: *.rst is migrated to *.md.
  • In the graph, the languages are sorted in descending order from top to bottom by number of lines at the time of the final tag.
    • If lines numbers are equal, the secondary sort criteria is the display name of language.
  • The command line option --width and --height specify the size of the graph in pixels.

    • The defaults are 1024 resp. 768.

    • If the value is less than than 600 resp. 400 or more than 32,767, it is rejected with the message:

      Value for option --xxx must be between XXX and 32767.

      Note: PNG could use sizes up to 2**31 - 1.

  • ❓ TBD: General layout, percentage used, maximum length of language before cut off, font to use, how to scale font, ...

Wireframe

Notes

The idea is to have graphs similar to the Jenkins SlocCount pluggin:

[roskakori]

@ropapermaker Assuming you are not going to finish this any more, I'm putting it back to the backlog so it can be revisited again in the future.