Initial discord remote auth support.

It works, but nothing is persisted yet as the user object needs some tweaking
especially the database side.

remoteauth/README.md

@@ -0,0 +1,54 @@
+# Discord Remote Authentication
+
+This library implements the desktop side of Discord's remote authentication
+protocol.
+
+It is completely based off of the
+[Unofficial Discord API Documentation](https://luna.gitlab.io/discord-unofficial-docs/desktop_remote_auth.html).
+
+## Example
+
+```go
+package main
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/skip2/go-qrcode"
+)
+
+func main() {
+	client, err := New()
+	if err != nil {
+		fmt.Printf("error: %v\n", err)
+
+		return
+	}
+
+	ctx := context.Background()
+
+	qrChan := make(chan *qrcode.QRCode)
+	go func() {
+		qrCode := <-qrChan
+		fmt.Println(qrCode.ToSmallString(true))
+	}()
+
+	doneChan := make(chan struct{})
+
+	if err := client.Dial(ctx, qrChan, doneChan); err != nil {
+		close(qrChan)
+		close(doneChan)
+
+		fmt.Printf("dial error: %v\n", err)
+
+		return
+	}
+
+	<-doneChan
+
+	user, err := client.Result()
+	fmt.Printf("user: %q\n", user)
+	fmt.Printf("err: %v\n", err)
+}
+```