add lint command to Makefile

Makefile

@@ -2,14 +2,35 @@ PKG := github.com/lightninglabs/loop
 
 GOTEST := GO111MODULE=on go test -v
 
+GO_BIN := ${GOPATH}/bin
+
+GOFILES_NOVENDOR = $(shell find . -type f -name '*.go' -not -path "./vendor/*")
 GOLIST := go list $(PKG)/... | grep -v '/vendor/'
 
+LINT_BIN := $(GO_BIN)/golangci-lint
+LINT_PKG := github.com/golangci/golangci-lint/cmd/golangci-lint
+LINT_COMMIT := v1.18.0
+LINT = $(LINT_BIN) run -v
+
+DEPGET := cd /tmp && GO111MODULE=on go get -v
 XARGS := xargs -L 1
 
 TEST_FLAGS = -test.timeout=20m
 
 UNIT := $(GOLIST) | $(XARGS) env $(GOTEST) $(TEST_FLAGS)
 
+$(LINT_BIN):
+	@$(call print, "Fetching linter")
+	$(DEPGET) $(LINT_PKG)@$(LINT_COMMIT)
+
 unit: 
 	@$(call print, "Running unit tests.")
 	$(UNIT)
+
+fmt:
+	@$(call print, "Formatting source.")
+	gofmt -l -w -s $(GOFILES_NOVENDOR)
+
+lint: $(LINT_BIN)
+	@$(call print, "Linting source.")
+	$(LINT)