Refactors Nix code to be even simpler.
nix-shell -A nrm # for a nrm development environment. nix-shell -A test # for an versioned integration test environment. nix-build -A <tab> # to build a package from the versioned test environment. nix-shell -A <tab> # for other shell options. nix-build -A <tab> # for other build options.