use goctl template to generate all kinds of templates

tools/goctl/util/head.go

@@ -0,0 +1,11 @@
+package util
+
+var headTemplate = `// Code generated by goctl. DO NOT EDIT!
+// Source: {{.source}}`
+
+func GetHead(source string) string {
+	buffer, _ := With("head").Parse(headTemplate).Execute(map[string]interface{}{
+		"source": source,
+	})
+	return buffer.String()
+}