Callbacks fixed for both button types.

bot.go

@@ -98,7 +98,7 @@ func (b *Bot) Handle(endpoint interface{}, handler interface{}) {
 	case string:
 		b.handlers[end] = handler
 	case CallbackEndpoint:
-		b.handlers["\f"+end.CallbackUnique()] = handler
+		b.handlers[end.CallbackUnique()] = handler
 	default:
 		panic("telebot: unsupported endpoint")
 	}

callbacks.go

@@ -70,7 +70,7 @@ type InlineButton struct {
 
 // CallbackUnique returns InlineButto.Unique.
 func (t *InlineButton) CallbackUnique() string {
-	return t.Unique
+	return "\f" + t.Unique
 }
 
 // CallbackUnique returns KeyboardButton.Text.