Pull more of the scripts to their own files

Fixes #19

nix/generate.nix

@@ -0,0 +1,27 @@
+{
+  writeShellApplication,
+  bash,
+  coreutils,
+  curl,
+  jq,
+  pup,
+}:
+
+writeShellApplication {
+  name = "generate";
+  runtimeInputs = [
+    bash
+    coreutils
+    curl
+    jq
+    pup
+  ];
+  text = ''
+    shopt -s globstar
+    for vars in distros/**/*.pkrvars.hcl.sh; do
+      bash "./''${vars}"
+    done
+    set -x
+    echo "BUILD=$(date "+%Y.%m.%d.%H")" >> build.env
+  '';
+}

nix/shellcheck.nix

@@ -0,0 +1,15 @@
+{ writeShellApplication, shellcheck }:
+writeShellApplication {
+  name = "shellcheck";
+  runtimeInputs = [
+    shellcheck
+  ];
+  text = ''
+    scripts=()
+    shopt -s globstar
+    for f in **/*.sh; do
+    	scripts+=("$f")
+    done
+    shellcheck -e SC2239 "''${scripts[@]}"
+  '';
+}