Use cobra for cli.

Signed-off-by: Lantao Liu <lantaol@google.com>

vendor/github.com/spf13/cobra/command_win.go

@@ -0,0 +1,26 @@
+// +build windows
+
+package cobra
+
+import (
+	"os"
+	"time"
+
+	"github.com/inconshreveable/mousetrap"
+)
+
+var preExecHookFn = preExecHook
+
+// enables an information splash screen on Windows if the CLI is started from explorer.exe.
+var MousetrapHelpText string = `This is a command line tool
+
+You need to open cmd.exe and run it from there.
+`
+
+func preExecHook(c *Command) {
+	if mousetrap.StartedByExplorer() {
+		c.Print(MousetrapHelpText)
+		time.Sleep(5 * time.Second)
+		os.Exit(1)
+	}
+}