some feature update

[yjf2002ghty]

demo: https://fairyground-new.vercel.app/

Minor changes:

1. added box for Threads, Hash, MultiPV
2. added info section to show current board FEN (useful for copying the game to other applications)
3. a pop up text to show the game reult

Major changes

1. added support for promotion and gating(for wall squares, seirawan gating are considered as promotion.) by making users input their choice in a browser prompt dialog
2. added support for viewing previous positions in the game. This allows user to analyze previous situations

Minor updates are small improvements so they don't have bugs (At least I haven't experienced any bugs). Major updates are large improvements that can create some hidden bugs or contain some not well-written codes. They need further maintaining.

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Name	Status	Preview	Comments	Updated (UTC)
fairyground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 26, 2023 3:11pm

[yjf2002ghty]

I've also removed "play" and "analysis" page as their functions are highly duplicated with "advanced" page.

[ianfab]

Thanks a lot! The support for promotions and gating is a really nice and very much needed addition.

To review it in detail will take more time. One comment though regarding the extra pages. What you now renamed to the index page was the only page originally and only recently I added the additional pages. My main goal was to simplify the interface, since fairyground is currently the only real link I have from the official website to quickly try out live what Fairy-SF is about, so it should in my mind more or less just take selecting a variant to immediately start playing or analyzing. However, I did not want to drop the original layout, because I still found it useful for expert users. So to me it would still be important to somehow keep both target groups in mind.

[yjf2002ghty]

I continued to write some quick & dirty codes to add the following features based on previous changes:

1. Time control system. I don't know whether a simple playground needs such function, but I think it's not bad to add more features except for those potential bugs.
2. A "play" page with the time control system (as index.html). The goal of this page is to allow users to start games immediately after selecting the variant by clicking "Start game" button. However I my idea on realizing it is to import "advanced" page and hide some elements. This makes the page looks weird, for example there are 2 scroll bars. The idea is only a quick workaround while itself is not perfect and needs improvement.

The code is not in good quality and the features, I think, may be unnecessary for this simple demo. So if you don't like changes above, you can disapprove them :) .

[yjf2002ghty]

Major update Now supports theme per variant & wall square display.

[ianfab]

Wow, thanks. I really like that the customization of the themes is configuration and not hard-coded, that makes it really flexible.

I would just have two small requests:

• Please run the formatting
• It looks like the SVG/CSS generation script is outdated now. Could you please update it or alternatively document how you generated the files?

[ianfab]

Thanks for all the additions. Are you planning to do further changes, or is this PR ready for review?

[ianfab]

Just to check back, are you planning to do any further changes to the PR and/or address my comments from above, or should I take over from here?