Feature proposal: Mermaid diagrams

[marcosh]

When generating html documentation, it would be nice to automatically render Mermaid diagrams.

For example, if some Haskell code contained a comment like

-- | Some docs with a diagram
-- ```mermaid
-- flowchart LR
--    Start --> Stop
-- ```

should render as

Some docs with a diagram

flowchart LR
   Start --> Stop

[Kleidukos]

Yes, I had the same idea for a Haddock plugin. Many new things will unlock when we can rework the architecture of Haddock in the near future, so thank you for opening this ticket. :)