Working creation of a letter

I had to use an address ID for 'to' and 'from' and then did really
weak-sauce inline HTML.

lob/cmd/letter-create/main.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"log"
+	"os"
+
+	"github.com/Gleipnir-Technology/nidus-sync/lob"
+)
+
+func main() {
+	to := flag.String("to", "", "")
+	from := flag.String("from", "", "")
+	file := flag.String("file", "", "")
+	color := flag.Bool("color", false, "")
+	use_type := flag.String("use_type", "operational", "")
+
+	// Parse the flags
+	flag.Parse()
+
+	key := os.Getenv("LOB_API_KEY")
+	if key == "" {
+		log.Println("LOB_API_KEY is empty")
+		os.Exit(1)
+	}
+
+	client := lob.NewLob(key)
+	ctx := context.TODO()
+	req := lob.RequestLetterCreate{
+		To:      *to,
+		From:    *from,
+		File:    *file,
+		Color:   *color,
+		UseType: *use_type,
+	}
+	letter, err := client.LetterCreate(ctx, req)
+	if err != nil {
+		log.Printf("err: %v", err)
+		os.Exit(2)
+	}
+	log.Printf("done. Letter: %s", letter.ID)
+}