Right now I have no idea how it works, but it builds with "stack
build" and serves something on localhost:3000. I am not exactly happy
that building and interactive development depends on "stack(1)"
instead of more familiar "cabal repl", but I can live with it.
It requires Postgres database running on the localhost, which is
configured in my NixOS configuration, and not inside of this
repository. Probably can be done better.