Add Makefile and fix pacman.go

Makefile

@@ -0,0 +1,25 @@
+.PHONY: fmt vet check githook
+
+STAGED_GO := $(shell git diff --cached --name-only --diff-filter=ACM | grep '\.go$$')
+STAGED_PKGS := $(shell echo "$(STAGED_GO)" | tr ' ' '\n' | xargs -I{} dirname {} | sort -u | sed 's|^|./|')
+
+fmt:
+	@if [ -z "$(STAGED_GO)" ]; then exit 0; fi; \
+	unformatted=$$(gofmt -l $(STAGED_GO)); \
+	if [ -n "$$unformatted" ]; then \
+		echo "$$unformatted: unformatted staged file"; \
+		exit 1; \
+	fi
+
+vet:
+	@if [ -z "$(STAGED_GO)" ]; then exit 0; fi; \
+	go vet $(STAGED_PKGS)
+
+check: fmt vet
+
+githook:
+	@mkdir -p .git/hooks
+	@echo '#!/bin/sh' > .git/hooks/pre-commit
+	@echo 'make check' >> .git/hooks/pre-commit
+	@chmod +x .git/hooks/pre-commit
+	@echo "Installed pre-commit hook: .git/hooks/pre-commit"