Assort doc files into appropriate subfolders for easier navigation

[moxian]

Summary

Infrastructure "The doc folder has been restructured for easier navigation"

Purpose of change

Making the docs easier to navigate, because they are a bit of a mess right now, and it's very hard to discover the file you want to read if you don't already know the filename.

Describe the solution

Have four distinct subfolders in doc/ directory:

• compiling c++ - for all things C++.
• JSON - for all things JSON. Technical documentation on how to add content.
• design-balance-lore - for design-level documentation on what content to add.
• user-guides - for the few doc pages that we expose to the end-user

Move the doc files into one of the four folders above, if appropriate

Grep codebase for .md string, and update the old links to point to new paths, when appropriate.

Describe alternatives you've considered

• use different names for the folders, such as code for c++ and content for JSON. But in the end I decided that content is a bit too ambiguous with design, and I didn't want to create an extra folder level such as content/design/ vs content/json_reference because that felt unfair compared to a single level of C++.
  • Edit: changed to c++ anyway due to comments

Testing

Clicked around the docs in my branch on github - https://github.com/moxian/Cataclysm-DDA/tree/doc-shuffle . Seems to work but obviously was not able to check every link..

(I'm also hoping we have a CI check that'd yell at me if I missed something, but I'm not sure we do..)

Additional context

The former "Lore" folder was renamed to design-balance-lore because, turns out, it covered the design and balance aspects of the game pretty thoroughly, and was not focused exclusively on the narrative as the name would suggest.

The problem I was originally trying to solve here is that it was invariably taking me way more time than neccessary to locate instructions on how to use astyle/clang-tidy/other things inside DEVELOPER_TOOLING.md to the point that by now I have memorized how to actually use them, but I would still struggle locating the docs. This stemmed from the fact that DEVELOPER_TOOLING.md is situated in the sea of completely unrelated json docs, and one needs to know the exact name beforehand in order to find it.
So I simply moved DEVELOPER_TOOLING.md closer to the compiler-related docs in COMPILING/. And then moved CODE_STYLE.md there as well, because of course that's directly related (and if you're doing json changes you don't care about that one)

But then the next logical step is to move json-related docs to the json-named folder... and design-related files design folder... and here we are...

[github-actions]

Auto-requesting reviews from non-collaborators: @jbytheway

[Procyonae]

While I appreciate we barely have any C++ docs lumping them into compiling seems weird to me, I imagine peeps who find the compiling docs originally through github links would then outright ignore that folder once they're setup. (just renaming the folder to c++ would be fine imo)
On that topic this will need someone with wiki perms to go through and fix any doc links that got moved after it's merged. (Or we could just fina remove the wiki and move the rest to docs which I would have done by now if I had perms)