Remove "-exe" suffix of executable from package.yaml

This suffix looks unnatural in Unix world.

Fix main/Main.hs to print text, not <<loop>>

Change default license from BSD3 to AGPL3

I doubt I will ever bother to sue anybody over license of my haskell libraries,
but intentions matter, aren't they?

Drop hedgehog from dependencies of tests

I don't really like groundhog, and I see absolutely no reason why it would be
default dependency for tests.

Extend list of default dependencies with ubiquitous stuff

Replace reference to github repository with sourcehut

Setup treefmt/alejandra in containing directory

Configure treefmt(1) to reformat Nix files with alejandra(1)

Not that I like style of alejandra(1) or I like its advertisements,
but it seems to be best-maintained reformatter around.

Add treefmt.toml to automatically reformat sources

Additionally, tweak make package derivation fail to build if sources is
formatted incorrectly.

Move definition of "main" into the library

It increases library size in case library has any use on its own, but makes
development in "ghci" so much more convenient.

Drop "use_hpack" configuration option

hpack is so much better is any way than obscure "cabal" format, I don't know
why would anybody would prefer raw "cabal".

Update sources & compiler

ci: Also test on MacOS

Use ghc901 && Update the sources

ci: Update cachix and install-nix actions

[#25] Add step name and update run command to be multiline (#26)

Allow user to select library or executable (#22)

* Allow user to select library or executable

* Need to dedent the endif in default.nix

* Use choice variable for add_executable_section

* Use matrix strategy in github actions to test all combinations

* Use argstr, not attr

* Use double quotes

* Use multiline string operator

Co-authored-by: Utku Demir <me@utdemir.com>

* Use forward slash to split cookiecutter command up a bit

Co-authored-by: Utku Demir <me@utdemir.com>

* Remove chomping character from multi-line yaml

* Switch to yes/no use_hpack prompt, no multiline github action

Co-authored-by: Utku Demir <me@utdemir.com>

Actually run the build on the CI

Fix markdown link for hpack

Add some documentation for hpack; fix default.nix template