Make python/default.nix and lua/default.nix to replace
prog/default.nix for each respective language's packages
Move dev tools from prog into emacs/default.nix since that's what
they're relevant for.
Add some extra useful python packages (numpy, scipy, xarray,
matplotlib)
Add yamllint for YAML, associated flymake-yamllint for Emacs, remove
flymake-eslint since I'm not using it
Add lua-language-server and bash-language-server
Evie Litherland-Smith