Add makefile to simplify some tasks

Makefile

@@ -0,0 +1,28 @@
+BINARY = "build/wings"
+
+all: $(BINARY)
+
+$(BINARY):
+	go build -o $(BINARY)
+
+cross-build:
+	gox -output "build/{{.Dir}}_{{.OS}}_{{.Arch}}"
+
+.PHONY: install
+install:
+	go install
+
+test:
+	go test `go list ./... | grep -v "/vendor/"`
+
+coverage:
+	goverage -coverprofile=coverage.out ./...
+	go tool cover -html=coverage.out
+
+dependencies:
+	dep ensure
+
+install-tools:
+	go get -u github.com/golang/dep/cmd/dep
+	go get -u github.com/mitchellh/gox
+	go get -u github.com/haya14busa/goverage