Implement CLI scaffold

cmd/mailfull/command/main.go

@@ -0,0 +1,13 @@
+package command
+
+import (
+	"github.com/mitchellh/cli"
+)
+
+// Meta is for `*Command` struct.
+type Meta struct {
+	UI         *cli.BasicUi
+	CmdName    string
+	SubCmdName string
+	Version    string
+}