[Feature Request] Add Support for Setting a Base URL

[usernane]

In many cases, AJAX Request is usually sent to same server which having one base URL but the request is usually go to different end point. Currently, the developer have to set the base URL for every AJAX call. Instead, it is better to have the instance uses one base URL for all requests.

The base should be set in two ways, eather extracted from the base tag of the page or set manually using a method such as AJAXRequest.setBase