Linear thread styling

[erlend-sh]

Would you accept a PR that adds support for forum threads with linearly ordered comments as an alternative display mode for boards (communities) that opt into it?

Basically like LemmyBB, but in a modern style closer to Discourse/NodeBB rather than phpBB.

Certain modes of discussion are better served by a linear flow, e.g. troubleshooting or feature ideation. There is however no reason why such discussion boards shouldn't co-exist with nested discussion boards on a singular instance & interface.

Examples:
https://users.rust-lang.org/t/pattern-to-use-when-avoiding-arc-or-similar-smart-pointers/95927/
https://users.rust-lang.org/t/cargo-release-took-8h-while-debug-finishes-in-25s/96015/
https://internals.rust-lang.org/t/idea-implied-enum-types/18349
https://internals.rust-lang.org/t/variadic-generics-design-sketch/18974/