Full Nix and project infrastructure rework

[sir4ur0n]

So this ends up being a HUGE PR, sorry about that, it's never convenient when exploring infrastructure rework 🙇

Hopefully exhaustive list of changes or impacts of this PR:

• Build now relies on Stack both for developers and CI (previous haskell.nix infrastructure meant developers used Stack and CI used haskell.nix, and haskell.nix provides poor developer experience with Stack, see their documentation for more information)
  • Removing haskell.nix also means removing the sluggishness caused by immaterializations, so shells should be faster
• Stack integration should be much better now: commands like stack build, stack test, stack repl funflow, stack haddock, stack ide targets, etc., just work
• Haskell Language Server integration should be much better now: I removed hie.yaml as the project is now a standard Stack project, which HLS (via hie-bios) auto detects correctly
  • E.g. code completion, documentation display, navigation, typechecking, work in all libraries, including in tests!
• I copied and homogenized LICENSE files in each package
• Some packages had a package.yaml (i.e. Hpack), some directly had a xx.cabal file (i.e. Cabal), so I homogenized to a package.yaml for each package, and I also versioned all generated cabal files (it's the recommended way)
  • cas-store gave me a hard time because there is some OS-specific logic which I had to translate to Hpack, but I think I somehow managed
• I updated the Stackage resolver from 16.16 to 18.13.
  • Many dependencies are thus more up to date
  • GHC version thus bumped from 8.8.4 to 8.10.7
  • I also updated the extra-dependencies, in particular hvega and IHaskell
  • A few dependencies no longer need specific pinning (e.g. sqlite-simple)
  • A few minor code changes were required (e.g. add File to imports of Path in various Haskell files and notebooks, e.g. funflow/test/flows/TestFunflow.hs)
• Nix dependencies are now managed by Niv
  • It makes updating them easier
  • I have pushed jupyterWith dependency which was hardcoded to Niv depency too
• Reformatted Haskell code (which unfortunately leads to a big diff as many files were not formatted 😞 )
• Reworked the documentation according to all other changes
• Documented use of Direnv to improve Shell integration with Nix
• Fix broken Haddock for funflow-examples/makefile-tool/src/Types.hs
• Reformat all Nix files

• Build documentation and pages
• Check that test failure fails CI
• Move jupyterWith dependency to Niv (currently hardcoded)
• shell.nix seems to build docker-client and funflow (because of overlays?)
• Document using Direnv (and nix-direnv) for smooth shell integration
• Do a round of documentation
• Squash all commits and reuse the PR description in commit message

Closes #193

[GuillaumeDesforges]

Very nice work! 🎉

[dorranh]

Thanks for preparing this, @sir4ur0n - I know it was a lot of work! The changes here make sense to me and really do improve the experience of working on the project. HLS integration works way better and is much faster than it previously was. The only thing which would be nice in the future is breaking out the global formatting run into a separate PR to make the changes more readable. LGTM though - please feel free to squash and merge 🙂

[sir4ur0n]

I have reworked the commit tree, now there are 2 commits:

• the major commit with all the changes except the reformatting
• reformatting