Assorted Nix development shells

A bunch of Nix shells I've put together for development in languages from Python to Haskell, to frameworks like Elm.

Some of these are works in progress. If you have any queries open an issue and I'll try help out :)

1. Install Nix: https://nixos.org/nix/
2. Run nix-shell _.nix or copy shell as default.nix into relevant development environment