docs: small overall documentation improvements

[ThomasFrans]

General improvements to documentation and code clarity.

Describe your changes

• Add documentation comments to various items
• Change web API return types from bool/Option to Result
• Create helper functions with descriptive names instead of comments
• Remove redundant/confusing types
• Fix some documentation comments as instructed by cargo doc
• Rename variables to clear names

Checklist before requesting a review

• Documentation was updated (i.e. due to changes in keybindings, commands, etc.)
• Changelog was updated with relevant user-facing changes (eg. not dependency updates,
  not performance improvements, etc.)

[ThomasFrans]

I'm adding documentation because I like to work on the project with cargo doc --document-private-items open to get a general overview of a type's functionality. It also helps a lot with language server hover to quickly get information about functions. I think it's a help for new contributors as well to more easily get an idea of what does what.

I changed some code (most notably the web API return types) when it made sense instead of adding comments/documentation. For example, it makes more sense to return Result<(), ()> instead of bool because the former makes clear that the function can fail and how its status is returned, while the latter needs documentation to explain what true or false mean. I don't think it has any performance impact as the compiler probably optimizes the abstractions away.

[hrkfdn]

🙏