Add fourmolize script

Author: Soupstraw

scripts/fourmolize.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+if [[ $# -gt 0 ]]; then
+  case "$1" in
+    --changes)
+      # Run fourmolu on changes compared to `master`.
+      git diff --diff-filter=MA --name-only origin/master HEAD -- '*.hs'
+      ;;
+    *)
+      echo "Invalid option: $1" >&2
+      exit 1
+      ;;
+  esac
+else
+  git ls-files -- '*.hs'
+fi \
+  | { grep -v Setup.hs || true; } \
+  | xargs -r fourmolu -m inplace
+
+git diff --exit-code