Add format and check targets + integrate into CI

Makefile

@@ -4,7 +4,7 @@ GOPATH  := $(shell go env GOPATH)
 LDFLAGS := "-X 'main.Commit=$(COMMIT)' -X 'main.Version=$(VERSION)'"
 VERSION := $(shell cat ./version)
 
-all: run install build clean
+all: run install build clean format check
 
 run:
 	go run -ldflags=$(LDFLAGS) $(ABRA)
@@ -17,3 +17,9 @@ build:
 
 clean:
 	rm '$(GOPATH)/bin/abra'
+
+format:
+	gofmt -s -w .
+
+check:
+	test -z $$(gofmt -l .) || (echo "gofmt: formatting issue - run 'make format' to resolve" && exit 1)