More flexible literate Haskell extensions (Trac #9789), summary on wiki

[Merijn Verstraaten]

As requested on my ticket I summarised the entire proposal on the wiki here: https://ghc.haskell.org/trac/ghc/wiki/FlexibleLiterateExtension

I don't expect a lot of disagreement on discussion, aside from minor bike shedding on the flavour of the extension. I've started implementing this already. I'm open to bikesheds on exact extension, as it shouldn't affect the implementation.

Unless there's any vehement objections, I'll produce a diff on fabricator asap.

Cheers,
Merijn