feat: support dark mode

[OnceUponALoop]

Added support for dark mode with the auto_dark option to address #33

When this option is set the module will generate a second copy of the diagram in dark mode using the /dsvg server option.

In order to dynamically switch the image choice the module include a javascript file (mkdocs_puml/static/dark.js).

I just submitted a similar PR to the mkdocs_build_plantuml but I have to say, it was a lot easier to do in this project :+1:

Some things I would focus on when reviewing:

• dark.js I'm not a webdev by any means so it might need some love.

• puml.py/_stylize_svg() Now uses a css var lookup to set the background instead of fixing it to #ffff

Example Output

Here's an example of the output - I used the 2 cards to show they system state and the user preference so it's easier to follow along with the transition. You can find the whole example in my develop branch.

Note: Example include addition of the skinparam backgroundColor transparent directive to the puml exmaple diagrams.

[MikhailKravets]

That's fantastic @OnceUponALoop! I thought about similar implementation myself recently. Haven't you tried to run the dark theme with C4 diagrams?

I'll take a look more detailed a bit later this week. Anyway, great job and thank you for the contribution 🎉

[OnceUponALoop]

@MikhailKravets thank you for the awesome well structured project, it was easy to deal with :+1:

I was curious about the C4 diagrams, so I tested it out and i'm happy to report it seems to work with no issue. I think ultimately the support will depend on the theme chosen, I know some themes support dark mode and some don't :shrug:

C4 Diagrams Example

You can find the updated develop branch with C4 Diagram example.

[OnceUponALoop]

All the formatting changes are in the last commit, only after pushing did I realize I should have probably checked with you first on such a big style-only change.

Please let me know if that's ok and I can roll it back. To make the review less painful you can review the code changes with the commit filter and then review it independently

[MikhailKravets]

Hi @OnceUponALoop, yes, this looks nice! Thank you for the contribution. I'll put now everything together for a new release 🎉