docs: started typing _setup, Setup, and cfg

[ujisati]

Proposed change

Lua language server is really good at type checking, so I'm adding some type hints. I like types. You can agree or disagree on that one.

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Code quality improvements to existing code or addition of tests
• Documentation update

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:

Checklist

• I am running the latest version of the plugin.
• The code change is tested and works locally.
• There is no commented out code in this PR.
• The code has been formatted using Stylua (a .stylua.toml file is provided)
• The code has been checked with luacheck (a .luacheckrc file is provided)
• The README.md has been updated according to this change.
• The doc/telekasten.txt helpfile has been updated according to this change.

[lambtho12]

Thank you very much for improving the doc. It's great to see people starting to contribute a bit!
The issue was addressed in #332 that I just merged. Next time I will try to merge faster to avoid duplicate fixes.

Feel free to work with @TheTaoOfSu to improve the documentation so they can focus on more heavy lifting in the refactoring maybe?

[TheTaoOfSu]

I've done what I can to implement the LDoc/LuaDoc style that you used in your recent PR, but I've only applied it to comments I personally wrote when I started the refactor on the functions I've personally spent some time examining. These are primarily functions that are in lua/telekasten.lua in main, though many have been relocated in the refact branch, and it's pretty much exclusively focused on a basic overview of the function and specifying type and descriptions for all parameters and return values. Comments and documentation are definitely something I'd like to see improved, but it's a pretty low priority for me at the moment compared to the refactor itself. If you'd like to help in this department, I would definitely welcome and appreciate the effort.