Creates a new UrlLoader object.
url parameter specifies the URL to download. This parameter is optional and if specified loading starts immediately.
method parameter specifies the HTTP request method. It can be one of the values of UrlLoader.GET, UrlLoader.POST, UrlLoader.PUT or UrlLoader.DELETE.
The default HTTP method is UrlLoader.GET.
body parameter specifies the HTTP body data. This parameter is used only when the HTTP method is UrlLoader.POST or or UrlLoader.PUT.
After loading is finished, loaded data is stored at event.data field of Event.COMPLETE event as string.
url: (string, optional) URL to download. This parameter is optional and if specified loading starts immediately.
method: (string, default = "get") HTTP request method.
headers: (table, optional) HTTP headers.
body: (string, optional) HTTP body data. This data is sent as the message body of a request.