Motivation for this change

This documents most of the interesting functions in haskell.lib and some of the obvious ones. Most of this work was done during the documentation sprint at the NixCon 2017 hackathon in Munich. That's also why this uses the /* */ syntax, because that was the syntax we found was already in use in many of the 'core' library modules in /lib.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS - evaluation still works
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.