Added a Makefile for signing and versioning

Makefile

@@ -0,0 +1,23 @@
+VERSION := $(shell git describe --tags --candidates=1)
+GOBUILD_ARGS := -ldflags "-s -X main.Version=$(VERSION)"
+OS := $(shell uname -s)
+ARCH := $(shell uname -m)
+BIN := aws-vault
+FULL_BIN := $(BIN)-$(OS)-$(ARCH)
+SIGN_IDENTITY := "3rd Party Mac Developer Application: 99designs Inc (NRM9HVJ62Z)"
+
+.PHONY: build install sign clean
+
+$(FULL_BIN):
+	godep go build $(GOBUILD_ARGS) -o $(FULL_BIN) .
+
+clean:
+	-rm $(FULL_BIN)
+
+build: $(FULL_BIN)
+
+install: $(FULL_BIN)
+	cp $(FULL_BIN) $(GOBIN)/$(BIN)
+
+sign: build
+	codesign -s $(SIGN_IDENTITY) -v $(FULL_BIN)