Add cabal-based tooling

[jrp2014]

Thanks for keeping this great tutorial going.

A gratuitous PR. This allows scheme to be build using only cabal to complement the stack-based build.

At the same time, I

• extended .gitignore to match, and added a basic github workflow. (I also tried adding a haskell-ci based workflow for travis and github, but these failed to pick up the test files correctly (the golden test failed trying to parse <stdin> for reasons unknown)
• tweaked the sources to hush hlint and a load of compiler warnings. (These are a matter of taste and fancy, but there are now no warnings with almost all ghc warnings turned on.) The only one that I have left out is warnings to specify the sort of deriving to be used.
• made unqualified imports explicit (to make it easier to see where functions come from, which seems a win in a tutorial
• added (to the cabal file) a StrictData pragma to reduce the chance of space leaks. I didn't make IFunc in LispVal.hs a newtype which would further have reduced laziness.)

Anyway, I hope that you find some of these changes of some use.

[adamwespiser]

Wow, this is awesome! Thanks for the cleanup! I'm always glad to hear people are getting something out of it.

These changes go a long way to improve readability (eliminating warnings, using explicit imports, tossing unused variables is always a plus in my book 👍 )

In terms of HLinit/linter compliance, I don't really have preference there, just to err on the side of consistency for this project, which this PR does.

On gitlab actions, not sure why the golden files aren't being picked up: I started this project before github actions were a thing and since it's an educational tool, I think they are "nice to have" but not something I'll spend a lot of time on if the haskell-ci auto-generated files don't easily work.

I'm going to give tentative approval, and in a few days I'll squash and merge. Thank you!